Heat oven to 350ºF (or 325ºF for dark or nonstick pan). Generously spray bottom and sides of two 8-or 9-inch round cake pans with non-stick cooking spray.
Prepare and bake cake as directed on box for 8 or 9-inch rounds. Cool in pans 10 minutes. Remove to cooling rack. Cool completely, about 1 hour.
Cut one of the cake rounds horizontally in half, using long, sharp knife (the other cake round can be frozen for another occasion). On serving plate, place 1 layer, cut side up.
Spread with 1/2 of the thawed whipped topping; top with 1/2 of the strawberries. Add remaining cake layer, cut side down. Spread remaining thawed whipped topping over top of cake; top with remaining strawberries. Store covered in refrigerator, or serve immediately.