Make spaghetti according to instructions minus 3 minutes. You will want the spaghetti very al dente, as it will finish cooking in the oven and as it cooks will soak in some of the sauce flavor.
Slice meatballs, and put half on bottom of pan.
Mix spaghetti with sauce and half of the mozzarella cheese. You can add more cheese if you want. The cheese will hold the pie together. You don't want it too saucy.
Layer the spaghetti on top of the meatballs.
Add the remaining meatballs, and mozzarella.
Bake at 375 for 30 minutes or until the top cheese is melted.
Serve with remaining parmesan cheese.
Allow to sit for 10 minutes before cutting.