In saucepan combine soup, water, onion and pepper. Bring to boil, stirring occasionally. Pour half of mixture into greased 1 1/2 quart casserole. Make 3 layers in casserole, using rice (right from box), peas and tuna. Add remaining soup. Sprinkle with grated cheese. Bake covered at 375ºF. for 20-25 minutes cut through mixture with knife after baking 10 minutes.