Your lunch and dinner should comprise of all the major nutrients like proteins, a little amount of carbohydrates and good amount of fiber. With fruits, one gets only fiber and carbohydrates and thus it is not really advisable unless one is going to consume milk or buttermilk or yoghurt along with it. Also the fruits should be a mix, rather than only banana, chickoo, grapes or mango. It may be worthwhile to consume only fruits, when roasted oats and a small amount of nuts like walnuts and almonds can be sprinkled on top.