In a saucepan, combine gelatin and cold water; let stand 5 minutes to soften.
Heat and stir over low heat just until gelatin dissolves. Remove from the heat; add sugar. Stir until dissolved. Stir in undrained strawberries. Chill until partially thickened. Fold in whipped topping.
Place cake cubes in a mixing bowl; pour strawberry mixture over cake and mix gently. Pour into an ungreased 8 inch square baking dish. Chill until firm.
Garnish with fresh strawberries and mint if desired.