For the meatballs: Put the bread in a small bowl and add just enough milk to cover. Let soak for 5 minutes.
Add the meat, cheese, parsley, salt, pepper, egg and soaked bread to a large bowl and mix lightly with your hands; do not overwork. Form the mixture into balls and place on a baking sheet.
Heat a large skillet over medium heat and add a healthy drizzle of olive oil. Working in batches, fry the meatballs in the skillet until all sides are golden brown, 2 to 3 minutes per side. Set aside.
For the marinara sauce: Heat the olive oil in a large saucepan over medium heat. Add the Italian seasoning and onions and sweat the onions until translucent, 5 to 10 minutes. Add the garlic and cook for 30 seconds, then add the tomatoes and meatballs, bring to a simmer and simmer for 30 minutes. Season with salt and pepper and garnish with fresh basil.
Serve the meatballs and marinara over your favorite pasta.