Prepare the Breadcrumb Mixture. Preheat the oven to 375°F. Line a rimmed baking sheet with foil and place a lightly greased, oven-safe wire rack on top. In a large bowl, combine the breadcrumbs and milk. Let stand for 3–5 minutes until the liquid is absorbed.
Mix the Burgers. Add the ground beef, ½ cup ketchup or barbecue sauce, seasoning salt, pepper, egg, onion, Worcestershire sauce, and garlic to the breadcrumb mixture. Gently mix until just combined, being careful not to overwork the meat.
Shape, Bake, and Glaze. Divide the mixture into 6 equal portions and shape into ¾–1-inch-thick patties, slightly wider than the buns. Press your thumb into the center of each patty to create a shallow indentation that helps prevent puffing. Arrange on the prepared rack, leaving space between them. Bake for approximately 20 minutes, then brush the tops with the remaining ¼ cup ketchup or barbecue sauce. Continue baking for 5–10 minutes, or until the centers reach 160°F (71°C).
Add Toppings and Serve. If desired, add a slice of cheese during the final 1–2 minutes of baking. Let the burgers rest for 3–5 minutes, then serve on toasted buns with lettuce, tomato, red onion, pickles, and your favorite condiments, or enjoy without buns.