Finely chop one-third of the onion; thinly slice the remaining onion. In a large bowl, combine chopped onion, egg, dried tomato, bread crumbs, and 1 teaspoon of the Italian seasoning. Add ground beef; mix well. Shape into 12 meatballs. In a large skillet, cook meatballs in hot oil over medium-high heat until brown on all sides. Carefully drain off fat. Transfer meatballs to a 4 1/2- or 5-quart slow cooker.