grated Parmesan cheese for servingif desired (not vegan)
Heat the olive oil in a large nonstick skillet set over medium heat. Add the onion and cook, stirring occasionally, until the onion is tender, about 5 minutes. Add the garlic, oregano and red pepper flakes, and cook for 1 minute.
Stir in the crushed tomatoes, petite diced tomatoes, salt and pepper. Transfer to a slow cooker. Stir in the chickpeas.
Cook on LOW for 6 to 8 hours or on HIGH for 4 to 5 hours.
Stir in the parsley. Season to taste with salt and pepper.
Serve over rice, pasta, or quinoa with grated Parmesan cheese, if desired.