Place egg, parmesan, breadcrumbs, garlic, seasoning, Worcestershire, salt, and pepper in a large bowl. Finely grate the onion into the mixture. Stir it together until it forms a thick paste.
Add the turkey to the bowl and work the mixture together gently. You don’t want to over mix the meatball mixture, but make sure that the turkey and seasonings are all mixed through.
Heat a large skillet over medium high heat. Add the oil to the pan and let it heat through.
Scoop desired size meatballs in uniform size. Place meatballs into the hot pan. Once you put them down, don’t move them.
Cook meatballs about 3-5 minutes per side, or until they’re browned. At this point you can do two different things with your meatballs:
Oven: preheat oven to 350°F. Transfer the meatballs to a baking sheet and bake until cooked through and the internal temperature is 165°F (about 10-15 minutes).
Stovetop: Add marinara sauce to the pan and stir carefully to coat the meatballs. Turn heat to medium, cover the pan and cook, stirring occasionally, until cooked through and the internal temperature is 165°F (about 10-15 minutes).