1. Preheat the oven to 350 F and spray an 11 x 7″ baking dish with nonstick spray. Add the olive oil to a large pan over medium heat on the stove. Add the onion, then sauté for 4-5 minutes or until it begins to turn translucent. Add the garlic and cook for an additional minute, before adding in the ground pork, oregano and salt. Cook the sausage until entirely browned and no pink remains, about 6-7 minutes. Break up the meat with a large wooden spoon as you cook it.
2. To the same mixture, pour in the pasta sauce and stir to combine. Remove from heat. Spread half of the sausage mixture evenly over the bottom of the prepared baking pan. Sprinkle 1 cup of the shredded mozzarella cheese over the top of the sausage mixture, followed by half of the ravioli from the package (it’s ok if the pasta is not touching each other).
3. Repeat the layers one more time, finishing with an extra sprinkle of mozzarella cheese over the top of the last layer of ravioli. Sprinkle the parmesan cheese over the top of the mozzarella. Spray a large piece of tinfoil with nonstick spray, then place the sprayed side of the foil over the casserole dish, tightly pinching the edges around the dish.
4. Bake the casserole in the oven for 35-40 minutes or until bubbling. Remove the foil from the top of the dish, turn the oven to broil and bake for another 1-2 minutes or until brown and bubbly. Take the casserole dish out of the oven and place on the counter to cool for 10 minutes before serving.

Leftovers, once cooled, can be stored in an airtight container in the fridge. The casserole can also be stored in the freezer, for up to 2 months. Thaw overnight in the fridge, then bake the casserole (covered) for an hour at 350 F.