Cook spaghetti according to package directions and drain.

Add butter to the warm spaghetti and stir until melted and evenly distributed.

In a bowl, whisk eggs and Parmesan cheese together.

Add the egg and cheese mixture to the spaghetti and mix well to combine.

Grease a pie dish with butter.

Press the spaghetti mixture into the buttered dish, forming a crust along the bottom and sides.

In a large pan, brown ground beef (or Italian sausage) over medium heat.

Add minced onion and green peppers (if using) and cook until tender.

Drain off any excess fat.

Stir in spaghetti sauce and heat through.

Spread ricotta cheese evenly over the spaghetti crust.

Top the ricotta with the meat sauce mixture.

Bake uncovered in a preheated 350 degree oven for 20 minutes, or until bubbly.

Sprinkle shredded mozzarella cheese on top.

Bake for another 5 minutes, or until the cheese is melted and bubbly.