Heat 1 tablespoon of olive oil in a large skillet over medium heat until it shimmers.

Add the thinly sliced onion and sauté, stirring occasionally, until softened and caramelized, about 5 to 7 minutes.

Push the onions to one side of the skillet and add the ground beef to the empty space. Break it up with a spatula and cook until fully browned with no pink, about 6 to 8 minutes.

Season the beef and onions with salt and freshly ground black pepper, mixing them together so the flavors combine.

Turn off the heat, mound the beef mixture in the center, place the cheese on top, and cover the skillet. Let the residual heat melt the cheese for 2 to 3 minutes.

Meanwhile, toast the hoagie rolls until golden.

Spoon the cheesy beef and onion mixture into the toasted rolls and serve immediately while hot.