In a large skillet over medium-high heat, brown ground beef, onion, and garlic. Cook until onion becomes clear and soft, approximately 20 minutes. Drain excess fat. Transfer meat mixture to crockpot. Add the tomatoes, tomatosauce, oregano, italian seasoning, and salt and pepper, stirring to break up stewed tomatoes. Cover and cook on Low for 7 to 8 hours or on High for 3 1/2 to 4 hours.
In the last 30 minutes turn on High if on Low. Stir in the cooked pasta, spinach, and cheese. Serve immediately when mozzarella cheese is melted.
Serves 6.