Preheat oven to 450 degrees. In large bowl, combine strawberries and 1/4 cup sugar. Stir gently until well combined. Set aside
For Cake, in a medium bowl, combine flour, cocoa powder, 1/4 cup sugar, and baking powder. Using a pastry blender, cut in margarine until mixture resembles coarse crumbs.
In small bowl, combine milk, egg or egg substitute, and vanilla. Add to dry ingredientsa nd stir just to moisten.
Spray an 8 inch round baking pan with cooking spray. Spread dough in pan, building up sides slightly. Bake for 15 to 18 minutes, or until a toothpick inserted near the center comes out clean. Cool for 10 minutes on wire rack. Remove cake from pan; place on serving plate.
To serve,, stir yogurt until smooth and creamy. Slice cake in half horizontally. Spoon half the strawberries onto bottom half of cake. Cover with top of cake. Spoon remaining strawberries and any juice on top of cake and dollop with yogurt. Serve warm or at room temperature.