Heat the olive oil in a medium skillet over medium heat. Add the onion and cook for 2 minutes. Add the mushrooms and cook until the onion is soft and the mushrooms are browned. Reduce the heat to low and add the garlic. Cook for 1 minute while stirring.
Spoon 1 cup of marinara sauce into the bottom of the crockpot. Top with a layer of ravioli.
Sprinkle with half the sauteed vegetables, all the Italian blend cheese, and a little Italian seasoning. Top with a layer of ravioli.
Spoon 1¼ cups of marinara sauce over the ravioli and sprinkle with Italian seasoning.
Top with the remaining sauteed vegetables, a layer of ravioli, the remaining marinara sauce, the mozzarella, and a little Italian seasoning.
Cover and cook on low for 3-4 hours.
Notes
Store leftovers in an airtight container in the refrigerator for up to 3 days.
Reheat in the microwave at reduced power for short intervals until warm.