In a large bowl, combine ground beef, breadcrumbs, egg, minced garlic, Italian seasoning, salt, and pepper. Mix gently with your hands until just combined—don't overmix or the meatballs will be tough.
Roll the mixture into 16-18 meatballs, about 1½ inches in diameter. Keep them roughly the same size so they cook evenly.
Heat olive oil in a large skillet over medium heat. Add meatballs and cook, turning occasionally, until browned on all sides, about 8-10 minutes. They don't need to be fully cooked through yet.
Pour the marinara sauce over the meatballs in the skillet. Reduce heat to low, cover, and simmer for 15-20 minutes until the meatballs are cooked through.
While the meatballs simmer, bring a large pot of salted water to a boil. Cook spaghetti according to package directions, usually 8-10 minutes. Drain well.
Serve the spaghetti on plates or in bowls, top with meatballs and sauce, and sprinkle with Parmesan cheese if desired. Enjoy with garlic bread if you have a little extra in the budget!