Mix the sugar and cornstarch in a large bowl.
Add the mango, rhubarb, lemon juice and ginger and toss to coat.
Mix the flour, rolled oats, coconut, brown sugar and butter in a large bowl.
Place the mango and rhubarb mixture into an 8x8 inch baking dish and pour the topping on.
Bake in a preheated 350F oven until it is bubbling and the top is golden brown, about 45 minutes.