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 1.5 quart casserole dish. Top with cheese. Bake in 400 oven for 20 minutes or until bubbly. Serve hot. Makes 6-8 servings, 0.75 cup each.