Preheat oven to 350 degrees. Mix soup and milk. In a 9 by 13 inch baking dish, combine the macaroni, tuna, soup/milk and salt and pepper. Mix well, and then top with cheese. Bake at 350 degrees for about 25 minutes, or until bubbly. Sprinkle with fried onions, and bake for another 5 minutes. Serve hot.