Spray the insert of large crock pot (I use a 7 quart) with non-stick cooking spray. In a separate bowl, stir the pasta sauce, diced tomatoes, and garlic together until combined.
Spoon 1/3 of the sauce mixture into the prepared crock pot. Top with 1/3 of the frozen ravioli. Sprinkle 1/3 of both cheeses evenly over the ravioli.
Repeat layers 2 more times, ending with the cheese. Cover with lid and cook on low heat for 3 to 4 hours or until heated through. Serve warm and enjoy!