Brown the ground beef in a skillet over medium-high heat for 6-8 minutes until no longer pink.

Sauté chopped onion and green bell pepper in the same skillet for 4-5 minutes until translucent.

Add diced tomatoes, Italian seasoning, salt, and pepper. Simmer for 15 minutes.

Cook spaghetti according to package instructions, about 8-10 minutes, until al dente.

Combine softened cream cheese and melted butter in a bowl, then mix in Parmesan cheese and milk.

Stir in garlic powder, salt, and pepper to the cream cheese mixture.

Toss drained spaghetti with the cream cheese mixture.

Layer half of the creamy spaghetti mixture in a greased baking dish, followed by the meat sauce and half of the mozzarella.

Repeat layers with remaining ingredients.

Bake at 350°F (175°C) for 25-30 minutes until cheese is bubbly and golden.

Let the casserole rest for 5-10 minutes before serving.