Preheat your oven to 375°F (190°C) and position the oven rack in the top third.

In a medium bowl, combine cream cheese, ricotta, Parmesan, garlic powder, and oregano until smooth and creamy.

Bring a large pot of salted water to a boil. Add uncooked spaghetti and cook for 2 minutes less than the package directions. Drain and return to the pot.

In a large skillet, cook Italian sausage and diced onion over medium-high heat until browned. Add minced garlic and red pepper flakes, cooking for another minute.

Transfer the sausage and onion mixture into the pot with spaghetti. Pour in the marinara sauce and toss until well coated.

Spread half of the spaghetti mixture in a greased 9x13-inch baking dish. Dollop with the cream cheese mixture, then add the remaining spaghetti.

Sprinkle mozzarella cheese over the top. Cover with foil and bake for 30 minutes.

Remove foil and switch oven to broil. Broil for 3-5 minutes until cheese is bubbly and golden brown.

Let cool for 5-10 minutes before slicing. Season with salt and pepper to taste before serving.