Preheat your oven to 175°C (350°F) and grease a 9×13-inch baking dish.
Cook the meat: In a skillet over medium-high heat, brown the ground beef until fully cooked. Drain any excess grease, then stir in the marinara sauce and simmer for 5 minutes.
Prepare the cheese layer: In a medium bowl, mix together the softened cream cheese, sour cream, garlic powder, salt, and pepper until smooth.
Assemble the base: Toss the cooked spaghetti noodles with the cream cheese mixture until thoroughly coated, then spread them evenly into the bottom of the prepared baking dish.
Add the meat and cheese: Pour the meat and sauce mixture evenly over the spaghetti layer. Top everything generously with the shredded mozzarella cheese and parmesan cheese.
Bake: Bake uncovered for 20 to 25 minutes, or until the cheese is completely melted, bubbly, and lightly golden on top.
Serve: Let it cool for 10 minutes before slicing and serving warm.