In a skillet over medium heat, cook 1 lb ground beef or sausage until browned. Add minced garlic, salt, pepper, and Italian seasoning, then drain excess grease.
In a bowl, combine marinara sauce and tomato sauce, then mix in the cooked meat.
Spread a thin layer of the meat sauce on the bottom of the crockpot.
Add a layer of frozen ravioli (about one-third of the bag).
Spoon about ⅓ cup ricotta cheese over the ravioli.
Sprinkle about ⅔ cup mozzarella and 2 tablespoons Parmesan cheese.
Repeat layers two more times, finishing with the remaining cheese on top.
Cover and cook on LOW for 4 hours or HIGH for 2.5 hours, until heated through and cheese is melted.
Turn off heat and let rest for 10 minutes before serving.