In a skillet over medium heat, cook the ground beef (or Italian sausage) with the chopped onion and minced garlic until the meat is browned and the onions are soft. Drain any excess fat.

Stir in the marinara sauce, undrained diced tomatoes, Italian seasoning, salt, and pepper to the skillet. Simmer the sauce for about 5 minutes to combine the flavors. Adjust seasoning if necessary.

Spread a thin layer of the meat sauce on the bottom of the slow cooker.

Arrange a single layer of frozen cheese ravioli over the sauce.

Spoon a layer of meat sauce over the ravioli.

Dot with spoonfuls of ricotta cheese and sprinkle with mozzarella and Parmesan cheese.

Repeat the layers until all ingredients are used, finishing with a layer of cheese on top.

Cover and cook on low for 4-6 hours or until the ravioli is tender and the lasagna is heated through.

Carefully scoop out servings of the ravioli lasagna. It may not hold its shape as well as traditional lasagna, but it will be just as tasty.

Garnish with fresh basil or parsley if desired before serving.