Preheat your oven to 350°F (175°C).
Cook the spaghetti according to package instructions until al dente. Drain and return to the pot.
Stir in the butter, Parmesan cheese, and beaten eggs into the spaghetti until well combined.
Press the spaghetti mixture into the bottom and up the sides of a greased 9-inch pie plate to form a crust.
In a skillet over medium heat, cook the ground beef, onion, and bell pepper until the beef is browned and the vegetables are tender. Drain any excess fat.
Add the garlic to the skillet and cook for another minute.
Stir in the tomato sauce, oregano, basil, salt, and pepper. Simmer for about 5 minutes.
Spoon the beef mixture over the spaghetti crust.
Sprinkle the mozzarella cheese on top.
Bake in the preheated oven for 20-25 minutes, or until the cheese is melted and bubbly.

Let the pie cool for a few minutes before slicing and serving.
Variations & Tips
For a lighter version, you can use ground turkey instead of beef. If you have picky eaters, consider blending the sauce to hide the vegetables. You can also add more vegetables like mushrooms or zucchini for added nutrition. For a cheesy twist, mix some ricotta cheese with the spaghetti crust. If you prefer a spicier pie, add a pinch of red pepper flakes to the sauce.