In 4-quart Dutch oven or 12-inch skillet, heat oil over medium heat.
Add onion and garlic; cook about 4 minutes, stirring occasionally, until onion is tender.
Stir in pasta sauce, tomato sauce and Italian seasoning.
Spray 5- to 6-quart slow cooker with cooking spray.
Place 1 cup of the sauce mixture in cooker.
Add 1 bag frozen ravioli; top with 1 cup of the cheese.
Top with remaining bag of ravioli and 1 cup cheese.
Pour remaining sauce mixture over top.
Cover; cook on Low heat setting 5 hours 30 minutes to 6 hours 30 minutes.
Before serving, sprinkle with parsley.
Ravioli will hold on Low heat setting up to 30 minutes.
Notes / Tips / Wine Advice:
Watching your fat? Be sure to compare the nutrition labels on various brands of cheese-filled ravioli; some are higher in fat than others—and lower-fat varieties are just as tasty.