Brown the Meat:
In a skillet over medium heat, cook the ground beef or sausage until browned. Drain any grease, then stir in the marinara sauce, garlic powder, Italian seasoning, and a pinch of salt and pepper. Let it simmer for 5 minutes.
Make the Creamy Filling:
In a medium bowl, mix cream cheese, ricotta, sour cream, and Parmesan cheese until smooth and creamy.
Prepare the Spaghetti:
Cook spaghetti noodles until just al dente. Drain and toss with olive oil to prevent sticking.
Layer the Casserole:
Lightly grease the inside of your slow cooker.
Spread a thin layer of meat sauce on the bottom.
Add half of the spaghetti noodles.
Spread half of the creamy cheese mixture.
Sprinkle some mozzarella cheese.
Repeat the layers, ending with meat sauce and mozzarella on top.
Cook:
Cover and cook on LOW for 4–5 hours or HIGH for 2–3 hours, until everything is melted, bubbly, and delicious.
Serve:
Garnish with chopped parsley and extra Parmesan cheese. Serve warm with garlic bread or salad.