Heat the olive oil in a skillet over medium heat. Add the onion. Cook, stirring often, until onion softens and begins to lightly brown, about 3 to 5 minutes. Add the garlic during the last 30 seconds of cooking.

While the onion cooks, put the ground beef, breadcrumbs, milk, egg, Parmesan cheese and Italian seasoning into a mixing bowl. Season with salt and black pepper. Add the cooked onions and garlic. Stir to just combine all the ingredients.

Shape into meatballs.

Put the meatballs into the skillet. Cook until golden brown on the bottom. Flip the meatballs over and continue to cook until cooked through, about 10 minutes in total. Use the meatballs as desired.