Prep Filling: In a large bowl, add the diced strawberries. Mash them lightly with the back of a fork to release some juice.
Fold & Chill: Gently fold the Cool Whip and mini marshmallows into the strawberries until well combined. Cover and refrigerate for 20 minutes.
Slice Cake: Using a sharp serrated knife, slice the angel food cake horizontally into three even layers. Set the top two layers aside.
Layer: Place the bottom cake layer on a serving platter. Spread a generous amount of the chilled strawberry cream over it. Place the middle layer on top and repeat the process.
Frost: Place the final cake layer on top. Use the remaining cream mixture to cover the top and sides of the cake completely.
Set: Refrigerate the cake for a minimum of 90 minutes before serving. This step is essential for the marshmallows to soften and the flavors to meld.
Decorate: Just before serving, garnish with fresh sliced strawberries if desired.