Preheat oven to 350°F.

Coat a 2 1/2 quart baking dish with nonstick cooking spray

In a large skillet, brown ground beef, onion, and green bell pepper over medium-high heat 6 to 8 minutes, or until beef is no longer pink, stirring frequently.

Drain off excess liquid.

Add spaghetti sauce, macaroni, water, garlic salt, and black pepper; mix well.

Pour the mixture into baking dish.

Cover and bake 25 minutes.

Uncover; top with Mozzarella cheese and bake 15 to 20 minutes more, or until cheese has melted and casserole is heated through.