1. Preheat oven to 350 F.

Make the meat sauce:

1. Heat oil in a large pot or 4 quart Dutch oven for 2 minutes over medium-high heat until the oil is sizzling hot. Add ground beef and cook for 5-7 minutes until browned.
2. Add onion and garlic. Stir well to combine and continue cooking for 3-4 minutes until tender.
3. Pour in tomato sauce, tomato paste, parsley, and salt. Stir well to combine. 
4. Bring the meat sauce to a simmer. Then, turn the heat down to low and let it simmer for 10 minutes uncovered. Set aside.

Assemble:

1. In a 9x13-inch casserole pan, layer the baked ravioli in the following layers:
   1. Sauce: Evenly spread 1 cup of the meat sauce on the bottom of the pan.
   2. Ravioli: Place a third (1/3) of the ravioli evenly in a single layer over the meat sauce.
   3. Cheese: Spread 1 cup mozzarella cheese evenly over the ravioli.
   4. Sauce: Spread another 1 cup of the meat sauce evenly on top. 
   5. Ravioli: Place 1/3 of the ravioli evenly in a single layer over the meat sauce.
   6. Cheese: Sprinkle 1 cup mozzarella cheese evenly over the ravioli.
   7. Sauce: Evenly spread the remaining of the meat sauce on top.
   8. Ravioli: Place the remaining 1/3 of ravioli in a single layer over the meat sauce.
   9. Cheese: Spread the remaining mozzarella cheese evenly over the ravioli and top with parmesan cheese.

Bake the ravioli:

1. Lightly grease a large piece of aluminum foil and cover the casserole pan with the greased side inside. Greasing the foil prevents the melted cheese from sticking to the foil while baking.
2. Bake the ravioli covered for 45-50 minutes. Then, remove the foil and bake uncovered for another 20 minutes or until the melted cheese turns golden brown and bubbly. Optionally, turn on broiler on high and broil for 3-4 minutes to get a crispy and brown cheesy crust. But keep a close eye on the broiler as things can burn quickly.
3. Let the baked ravioli cool for 10 minutes before serving. Sprinkle on some chopped parsley, if desired.