Begin by cooking the thin whole-wheat spaghetti according to the package instructions. Drain and set aside, reserving a little pasta water in case you need to loosen the sauce later.
In a large skillet over medium heat, add the minced yellow onion and sauté for 2-3 minutes until translucent. Add the lean ground beef (or turkey) and cook until browned. Season with kosher salt and black pepper, stirring to combine.
Once the meat is cooked through, add the minced garlic and cook for another minute. Then, pour in the spaghetti sauce and bring to a simmer. Let it cook for about 10 minutes, allowing the flavors to meld together.
In a mixing bowl, combine the skim milk, Neufchâtel cheese, sour cream, and Parmesan cheese. Whisk together until smooth and creamy.
Add the creamy mixture to the skillet with the meat and sauce. Stir well to combine, allowing the sauce to heat through and thicken slightly.
Add the cooked spaghetti to the skillet. Toss everything together, ensuring the pasta is well coated with the sauce. If the sauce is too thick, add a splash of the reserved pasta water to achieve your desired consistency.
Preheat your oven to 350°F (175°C). Transfer the spaghetti mixture to a baking dish and top with shredded mozzarella cheese. Bake for 20-25 minutes or until the cheese is melted and bubbly.
