Fill a large pot with salted water. Bring it to a rolling boil. Add the spaghetti noodles. Cook them until they are just al dente. Drain the water and set the pasta aside.

Place a large skillet over medium heat. Add the ground beef and chopped onions. Cook until the meat is no longer pink. Drain any excess grease from the pan to keep it light.

Add the diced green peppers and minced garlic to the beef. Stir them well. Cook for about five minutes until the peppers are soft. This builds a wonderful flavor base for the sauce.

Pour in the tomato sauce and diced tomatoes. Add the oregano, basil, salt, and pepper. Lower the heat and let it simmer for ten minutes. The sauce should become thick and fragrant.

In a separate bowl, combine the softened cream cheese and sour cream. Stir until the mixture is smooth. This is the "secret layer" that makes this recipe famous and very creamy.

Grease your 9x13 baking dish with butter or cooking spray. Preheat your oven to 350 degrees Fahrenheit. Having everything ready makes the assembly process much faster and easier for you.

Place half of the cooked spaghetti in the bottom of the dish. Spread the cream cheese mixture over the noodles. Use a spatula to get an even layer across the entire surface.

Pour the beef and tomato sauce over the cream cheese layer. Ensure it covers all the noodles. The sauce will soak into the pasta as it bakes in the oven.

Sprinkle the cheddar and mozzarella cheese generously over the top. Use more cheese if you like a golden crust. The mix of two cheeses adds great texture and flavor.

Place the dish in the oven. Bake for 30 minutes. The cheese should be melted and bubbling. Let it sit for five minutes before serving to help the layers set.