Combine biscuit mix,milk,egg,melted butter and chocolate.Mix to combine thoroughly.In a blender,combine strawberries and banana.Blend a few seconds,until semi liquid.Add to cake mixture and mix thoroughly again.Pour into a 23 cm square baking pan and bake at 350 deg.for about 30 minutes,until a toothpick stuck in the cake center comes out clean.(It is an extremely moist cake,so toothpick will always have some moisture on it.) Serve warm or cold..