Empty the strawberry gelatin into a large heatproof bowl. Pour 1 cup boiling water over the gelatin. Whisk continuously until completely dissolved and smooth.

Stir in 1 cup cold water. Cover the bowl and refrigerate. Chill until the gelatin is slightly thickened but not fully set, about 20 to 30 minutes.

While the gelatin chills, hull and dice the strawberries. Drain the crushed pineapple very well in a fine sieve or paper towels to remove excess juice. Measure the marshmallows and whipped topping.

When the gelatin has thickened, remove it from the fridge. Gently fold in the diced strawberries, mini marshmallows, whipped topping, and crushed pineapple. Add chopped nuts if using. Fold until evenly combined.

Pour the combined mixture into a large glass bowl or trifle dish. Smooth the top with a spatula. Refrigerate until fully set, roughly 2 hours.

Serve chilled. Spoon into bowls and garnish if desired.