Heat a large skillet to medium high. Add ground beef, Italian sausage, onions and garlic cook until browned about 8 minutes. Drain fat and add sauce and diced tomatoes, mix until combined.
Add a layer of meat sauce into the bottom of the slow cooker, then a layer of frozen ravioli, meat sauce and cheese. Then repeat until you run out.
Cook on high for 3-4 hours. Turn off slow cooker and let set 20 minutes. Sprinkle with Parmesan cheese and fresh basil.