Preheat the oven to 425 degrees. Line a baking sheet with parchment paper.
In a large mixing bowl add ground beef, oregano, garlic, onion, salt and pepper.
Place the breadcrumbs in the milk and allow them to sit for a minute to soften and absorb some of the milk. Drain any excess milk from the breadcrumbs and add them to the meat mixture. This milk and breadcrumb mixture is called a panade and helps to keep the meatballs soft and tender.
Crack an egg and add the egg to the meat mixture.
Cover your hands with the olive oil generously to keep the meat mixture from drying out when you mix the meat. Mix the meast just enough that the breadcrumbs and spices are distributed well into the mixture, but not to overmix. Using your hands over a spoon also helps you to keep from overmixing the meat.
Once the meat is mixed, with oiled hands portion the meat into about twelve equal sized meatballs. Give the meatballs a quick and gentle roll, then place each meatball on the baking sheet, leaving about 2 inches between meatballs.
Bake meatballs for 18-20 minutes. Flip the meatballs after about 10-15 minutes to help them to brown more evenly. Meatballs should be cooked all the way through and no longer pink in the center.
While meatballs are cooking, place tomato sauce in a covered pot with a lid on the stove and heat through until it is simmering.
Toss meatballs in the tomato sauce, and enjoy hot.
This recipe makes 12 large meatballs or 18 smaller meatballs. You can cut them down in size and make smaller meatballs but they will cook faster in the oven. Start checking them after about 10-15 minutes of cooking if making the meatballs smaller.
If serving as meatballs subs, I recommend rolling a smaller meatball as they stay on the bun a little easier.