Preheat oven to 350 degrees. Prepare a 9x13 casserole dish with nonstick cooking spray and set aside.
Cook spaghetti according to the package directions. Drain and then set aside.
Add your egg and parmesan cheese to your spaghetti and mix well.
In a skillet cook and crumble ground beef. Drain the fat and then add in marinara sauce. Once heated through add to your spaghetti and mix well.
Place your spaghetti into your prepared casserole dish. Top with mozzarella cheese and bake covered for 40-45 minutes. Allow to rest for 10 minutes then slice and serve.