In a 1 1/2quart casserole mix kidney beans, limas and corn, all drained. Mix in tomatoes. If they are in large chunks, cut slightly by hand or in mini food processor or blender. In a small bowl, mix finely crushed crackers and finely shredded cheese together. Sprinkle on top of casserole. Bake in a 350° preheated oven for approximately 30 minutes. If desired, remove casserole after 20 minutes, sprinkle with canned onions and return to oven for 10 minutes. Serves 4 to 6.