Cook noodles according to package directions, until tender. Drain. Add onion, salt, pepper, cottage cheese, imitation sour cream, water, and tuna. Mix well. Pour into 1 1/2 quart casserole dish. Top with cheese. Bake in 400 oven for 20 minutes or until bubbly. Serve hot. Makes 6-8 servings, 3/4 cup each.