In a large mixing bowl, combine ground meat, breadcrumbs, Parmesan cheese, egg, Italian seasoning, salt, and pepper. Mix until just combined and form small meatballs, about 1 inch in diameter.

In a large pot or Dutch oven, heat a tablespoon of oil over medium heat. Add the meatballs in batches to avoid overcrowding. Cook until browned on all sides, about 5-7 minutes. Remove the meatballs and set them aside.

In the same pot, add more oil if needed. Sauté chopped onions and minced garlic until fragrant and translucent, about 2-3 minutes.

Stir in the penne pasta, marinara sauce, and broth. Bring the mixture to a boil and then reduce to a simmer.

Once simmering, return the meatballs to the pot. Cover and let it cook for about 15 minutes, stirring halfway through, until the pasta is cooked and meatballs are heated through.

If using spinach, stir it in just before serving. It will wilt beautifully with the heat of the pasta.

Remove from heat, garnish with fresh basil, and serve warm with additional Parmesan cheese on top.