Preheat oven to 375 degrees.
In a large bowl, combine meat, bread crumbs, milk, ketchup, seasoning salt, pepper, egg and diced onion. Do not over-mix. Divide into 6 equal portions and form into burgers. I make the burgers the size of my buns!
Place on a rimmed baking sheet, covered in tinfoil and a rack lightly coated in cooking spray.
Brush burgers with ketchup or barbecue sauce. Use your meat thermometer to be sure your burgers are cooked Between 25 and 30 minutes. Cooking time will vary depending on the kind of meat you are using.
Cooking note: Instead of individual patties I have made one meatloaf shaped like a cylinder (the size of my buns). Once cooked, usually between 60 and 75 minutes. I cut the loaf into individual "burgers". Paint mixture on top of each slice and broil for a few minutes until sauce hardens or caramelizes. These taste fabulous also and are definitely worth a try.