Preheat the oven to 350°F/180°C.
In a large 12-inch skillet, cook and brown the ground beef/Italian sausage with the onions until no longer pink. Drain the fat, and stir in the pasta sauce. Set aside.
Cook the spaghetti noodles according to the package instructions. Drain and place into a large bowl. Fold in 1 beaten egg, 3 tbsp melted butter, garlic powder and half of the shredded parmesan cheese with the noodles. Stir until combined.
Lightly butter the inside of a large casserole dish. Gently place the noodle mixture in the bottom of the prepared dish. With the back of a spoon, lightly press the noodles into the sides of the dish to form a crust shape; leaving a slight cavity for the filling layers.
In a small bowl, mix together the ricotta cheese, the last half of the parmesan cheese, dried oregano, basil and parsley.
Scoop the ricotta cheese mixture into the top of the noodle crust and spread evenly.
Next, add a layer of the meat and pasta sauce mixture. Top with mozzarella cheese.
Cover lightly with a large piece of foil and bake in a preheated oven for 30 minutes. Remove the foil and bake uncovered for an additional 5 minutes or until the cheese is fully melted.
Carefully remove the spaghetti pie casserole from the oven and let it cool slightly before serving.