In mixing bowl combine beaten egg, bread crumbs, milk, chopped onion, salt, oregano, and pepper.
Add the ground beef and mix well.
Shape about 1/4 cup of meat mixture evenly around each cherry tomato to form round meatballs.
Place meatballs in a 13x9x2-inch baking pan.
Bake in a 375° oven for 25 to 30 minutes.