Preheat oven to 350 degrees F. Lightly grease a 2-quart baking dish; set aside. Cook spaghetti according to package directions; drain. Return to pan.
Meanwhile, in a large skillet, cook ground beef, onions, sweet pepper, and garlic over medium heat until meat is brown and onion is tender. Drain off fat. Stir in mushroom soup, tomato soup, and water.
Bring to boiling; reduce heat. Simmer, uncovered, for 10 minutes, stirring occasionally. Stir in 1-1/2 cups of the cheese, the salt, and black pepper. Stir in cooked spaghetti.
Transfer mixture to the prepared baking dish. Sprinkle with the remaining 1/2 cup cheese. Cover with plastic wrap and store in the refrigerator. Include baking instructions with the casserole.