Crockpot Ravioli Casserole

1 1/2 lbs lean ground beef
1 medium onion, chopped
2 garlic cloves, minced
1 28 oz can peeled tomatoes, in thick tomato puree
1 15 oz can tomato sauce
2 tsp Italian seasoning
1/4 tsp pepper
1 lb bow-tie pasta or fettuccine, freshly cooked
1 10 oz pkg frozen chopped spinach, defrosted and squeezed to remove excess moisture
2 cups ricotta cheese
1/2 cup freshly grated Parmesan cheese

In a large skillet over medium-high heat, cook the ground beef, onion and garlic, stirring often to break up lumps, until the meat loses its pink color, about 5 minutes. Tilt the pan to drain off excess fat, then transfer the beef mixture to a 3.5-qt slow cooker.Add the tomatoes with their puree, the tomato sauce, Italian seasoning, and pepper, stirring to break up the tomatoes with the side of a spoon. Cover and slow cook for 7 to 8 hours on low. Skim the fat from the surface of the meat sauce. Stir in the cooked pasta, spinach, ricotta and Parmesan cheeses, slow cook for 5 more minutes