Brown the hamburger over medium heat in a medium size skillet..
Add the onion, garlic and tomatoes and simmer for 5 minutes.
Add the spaghetti sauce, Italian seasoning, salt and pepper and let simmer another 5 minutes.
Place 1 cup of sauce on the bottom of 5 to 6 qt. slow cooker.
Add half of the frozen ravioli, half the remainder of sauce and then repeat.
Sprinkle with cheese.
Cook on low 4 hours or until ravioli is tender.