Empty the strawberry gelatin packet into a large heatproof bowl. Pour 1 cup boiling water over the gelatin and whisk until it dissolves completely.

Stir in 1 cup cold water. Cover the bowl and refrigerate until the gelatin is slightly thickened but not fully set, about 20 to 30 minutes. You want it tacky, like a loose custard.

While the gelatin chills, hull and dice the strawberries, and measure the marshmallows and whipped topping. Press the crushed pineapple in a fine sieve or cheesecloth to remove excess juice.

When the gelatin is thickened, fold in the diced strawberries, mini marshmallows, whipped topping, crushed pineapple, and chopped nuts if using. Fold gently so the marshmallows keep their texture and the whipped topping stays airy.

Pour the mixture into a large glass bowl or a trifle dish. Smooth the top with a spatula and refrigerate until fully set, about 2 hours.

Serve chilled. Spoon into dishes and enjoy right away.