Overnight Veggie and Cheese Casserole

Name: Overnight Veggie and Cheese Casserole
Prep time: 20 min
Cook time: 35 min
Total time: 780 min
Ingredients: 1 cup diced bell peppers (any color); 1 cup diced onions; 1 cup diced tomatoes, seeds removed (for less liquid); 2 cups chopped fresh spinach; 1 loaf of bread, cubed (day-old or slightly stale); 6 large eggs; 1 cup milk (dairy or unsweetened plant milk) (whole milk gives a richer custard; use almond or oat milk for dairy-free); 1 teaspoon salt (reduce for lower sodium); 1/2 teaspoon black pepper; 1 teaspoon garlic powder; 1 teaspoon onion powder; 1 cup shredded cheese (cheddar, mozzarella, or a mix) (use a firmer cheddar for sharper flavor or mild mozzarella for stretch)

By:

Olivia Parker

| Posted on:

March 14, 2026

Overnight veggie and cheese casserole dish with colorful vegetables and melted cheese.

Recipes

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I remember making this casserole when mornings were chaotic and I needed something that would feed a crowd with almost no effort. Overnight Veggie and Cheese Casserole is a custardy bread bake loaded with bell peppers, onions, tomatoes, spinach, and melty cheese. It’s assembled the night before, so all you do in the morning is pop it in the oven for a golden, sliceable dish that’s perfect for family brunches, busy weeknights, or meal-prep breakfasts.

If you like make-ahead comfort food, you might also enjoy the ease of the slow cooker garlic butter chicken and veggies for a hands-off entrée that pairs well with simple sides.

Why you’ll love this dish

This casserole wins because it balances convenience, nutrition, and crowd appeal. It uses inexpensive pantry and fridge staples: day-old bread soaks up a savory egg custard, while peppers, tomatoes, and spinach add color and vitamins. Make it the night before to save morning time. It reheats well, slices neatly for serving, and works for varied occasions from casual breakfasts to potlucks. Kids and adults usually like the familiar cheese-and-egg base, and it’s easy to customize to dietary needs.

The cooking process explained

Quick overview so you know what to expect: chop the vegetables and cube the bread, whisk eggs with milk and seasonings, toss everything together with most of the cheese, refrigerate overnight for the bread to absorb the custard, then bake until set and golden. Total active prep is about 20 minutes; the overnight soak does the heavy lifting.

What you’ll need

1 cup diced bell peppers (any color)
1 cup diced onions
1 cup diced tomatoes, seeds removed for less liquid
2 cups chopped fresh spinach
1 cup shredded cheese (cheddar, mozzarella, or a mix) — use a firmer cheddar for sharper flavor or a mild mozzarella for stretch
6 large eggs
1 cup milk (dairy or unsweetened plant milk)
1 teaspoon salt
1/2 teaspoon black pepper
1 teaspoon garlic powder
1 teaspoon onion powder
1 loaf of bread, cubed (day-old or slightly stale works best)

Notes: whole milk gives a richer custard; use almond or oat milk to keep it dairy-free. For lower sodium, reduce the salt and use a low-sodium cheese.

Step-by-step instructions

Preheat your mindset: this is mostly hands-off after assembly. Gather and prep ingredients first.
In a large bowl, combine the diced bell peppers, diced onions, seeded tomatoes, chopped spinach, and cubed bread. Mix gently to distribute the bread pieces evenly.
In a separate bowl, crack in the eggs and add the milk, salt, black pepper, garlic powder, and onion powder. Whisk until smooth and slightly frothy.
Pour the egg mixture evenly over the bread and vegetable mixture. Stir gently so the liquid reaches all the bread cubes. Press down lightly with a spatula to help absorption.
Fold in the shredded cheese, keeping back a handful to sprinkle on top for a bubbly golden crust.
Cover the bowl tightly with plastic wrap and refrigerate for at least 6 to 12 hours so the bread becomes fully saturated.
When ready to bake, preheat the oven to 350°F (175°C). Grease a baking dish and transfer the soaked mixture into it, smoothing the top and sprinkling the reserved cheese over.
Bake for 30 to 35 minutes, until the center is set and the top is golden brown. A toothpick inserted near the center should come out mostly clean.
Let the casserole rest for 5 to 10 minutes before slicing; resting helps the pieces hold together for cleaner slices.

Best ways to enjoy it

Serve warm in squares with a simple green salad and mustard vinaigrette, or spoon a tomato-chive salsa on the side for brightness. For a cozy combo, pair with roasted potatoes or steamed asparagus. If you want a protein boost, serve with a side of grilled tofu or a lightly dressed bean salad. For an all-in-one brunch, set alongside fresh fruit and crusty bread.

If you like make-ahead mains as much as I do, check out this comforting slow cooker garlic butter chicken and veggies for another simple, hands-off recipe idea.

Storage and reheating tips

Refrigeration: Cool the casserole to room temperature within two hours of baking. Store covered in the refrigerator for 3 to 4 days.
Reheating: Reheat individual slices in the microwave for 60 to 90 seconds on medium power, or reheat a whole dish in a 325°F oven until heated through (about 15 to 25 minutes depending on size). Reheat until the internal temperature reaches 165°F for safety.
Freezing: Freeze baked portions tightly wrapped for up to 2 months. Thaw overnight in the refrigerator before reheating in the oven to preserve texture.
Food safety: Do not leave the egg-based mixture at room temperature for longer than two hours before refrigerating. Label and date leftovers.

Pro chef tips

Use day-old bread. Stale bread soaks up custard without turning mushy. If your bread is fresh, toast cubes lightly for 8 to 10 minutes.
Remove tomato seeds. That keeps the bake from becoming watery.
Press, but don’t drown. Press down the mixture so liquid reaches all cubes, but avoid smashing every piece flat. You want some air pockets for a light custard.
Cheese distribution matters. Folding most of the cheese into the mix and reserving some for the top gives a molten interior and a golden crust.
Test for doneness at the center. If the edges are set but the middle jiggles, give it another 5 minutes. Resting will finish the set.

Flavor swaps

Mediterranean: Swap the cheddar for crumbled feta and add chopped sun-dried tomatoes and olives. Omit garlic powder and use a pinch of oregano.
Southwest: Add a diced jalapeño, swap half the cheddar for pepper jack, and fold in a tablespoon of chopped cilantro before baking.
Dairy-free: Use unsweetened plant milk and a dairy-free shredded cheese. Increase seasoning slightly for depth.
Gluten-free: Replace the bread with cubed gluten-free loaf or use torn cooked sweet potatoes for a grain-free version.

Common questions

Can I assemble and bake the same day?

Yes. If you’re short on time, let the assembled casserole sit at room temperature for up to 30 minutes while your oven preheats, or for a firmer texture refrigerate for 1 to 2 hours before baking. Overnight chilling, however, yields the best custard texture.

Can I use frozen vegetables?

You can, but thaw and drain them well. Excess moisture from frozen vegetables can make the casserole watery. Best practice: sauté briefly to remove extra water before mixing.

How do I know when it is fully cooked?

The center should be set with a slight wobble, not liquid. A toothpick or knife inserted into the middle should come out mostly clean. After a 5 to 10 minute rest, it will finish setting.

Can I make this vegetarian or vegan?

This recipe is already vegetarian. For vegan, use a chickpea flour batter or a commercial egg replacer, plant milk, and dairy-free cheese. Texture will be slightly different but still satisfying.

What if my casserole is too soggy after baking?

Next time, reduce the milk by 2 to 3 tablespoons or use firmer bread toasted first. If it’s soggy immediately after baking, return to the oven for 5 to 10 minutes at 350°F to dry it out slightly.