Gather all ingredients. Preheat the oven to 350°F (175°C). Spray a 9x13-inch baking dish with cooking spray; set aside.

Boil spaghetti in generously salted water until cooked through but still firm to the bite, 8 to 10 minutes. Drain and set aside.

While pasta cooks, stir cream cheese, sour cream, and 1 cup of mozzarella cheese together until combined; set aside.

Heat olive oil in a large high-sided skillet over medium-high heat. Add beef in large chunks and cook, undisturbed, until lightly browned, about 2 minutes.

Add onion, garlic, Italian seasoning, salt, and pepper. Continue to cook, breaking up meat into smaller pieces with a wooden spoon and stirring occasionally, until almost cooked through, about 3 minutes.

Remove from heat and tilt the pan to pool grease onto one side, keeping the beef mixture on the other. Use a spoon to remove grease; discard grease once cooled.

Add marinara to beef mixture in skillet; stir until combined. Add reserved spaghetti. Fold and stir until well coated in sauce.

Transfer ½ of the pasta mixture to prepared baking dish. Spread sour cream mixture over pasta mixture, then top with remaining pasta mixture.

Sprinkle the remaining 1 cup mozzarella evenly over spaghetti mixture. Cover loosely with aluminum foil and place baking dish on a baking sheet.

Bake in preheated oven until cheese has melted, about 30 minutes. Remove aluminum foil and sprinkle top with Parmesan cheese. Increase oven temperature to broil.