In a large bowl, mix together the ground beef or turkey, breadcrumbs, Parmesan, egg, minced garlic, Italian seasoning, salt, and pepper. Get in there with your hands and mix until combined. Shape the mixture into small meatballs, about one inch in diameter.

Heat a large skillet over medium heat and add a drizzle of olive oil. Place the meatballs in the skillet and cook for about 8-10 minutes, turning occasionally until they're brown all over.

Remove the meatballs from the skillet and set aside. In the same skillet, add more olive oil if needed, and sauté the diced onion until soft, about 3-4 minutes. Add the minced garlic and cook for an additional minute.

Pour in the crushed tomatoes, add sugar, Italian seasoning, salt, and pepper, and stir. Bring the sauce to a gentle simmer. Add the meatballs back into the skillet for another 10-15 minutes.

While the sauce is simmering, cook spaghetti according to the package instructions. Drain and toss with a little olive oil to prevent sticking.

Plate the spaghetti, top with the meatballs and sauce, and garnish with fresh basil or parsley if desired.