Preheat oven to 350 F. Lightly grease a 9x13-inch baking dish with non-stick cooking spray.
Cook the spaghetti noodles as directed. Drain the water and return the noodles to the pot.
In a large mixing bowl, combine the egg, grated Parmesan cheese, 1 cup of the shredded mozzarella cheese and the Italian seasoning. It will be like a paste. Scrape it into the cooked pasta noodles and mix to combine and coat the noodles.
Transfer the tossed noodles into the baking dish and even them out. Top with the pre-cooked, frozen meatballs.
Pour the marinara sauce over the top, then the rest of the shredded mozzarella.
Bake in the preheated oven for 30 to 35 minutes, or until meatballs are cooked and warmed through. Top with shredded fresh basil garnish.
Serve Baked Spaghetti & Meatballs with side salad or veggies.