Heat oil in a small skillet over medium heat. Add the onions, cooking for 2 minutes. Add the garlic, cooking one minute more. Cool.
Crumble ground chuck into medium bowl. Add onion and garlic mixture, milk, potato flakes, Worcestershire sauce, salt and pepper. Gently combine the ingredients well. Shape meat into four oval patties. Refrigerate.
Combine apple butter and ketchup with a whisk until well blended. Cover and set aside.
Coat unheated grill grate with no-stick cooking spray. Heat grill to medium-high (350° to 400° F). Grill burgers 4 to 6 minutes per side or until juices run clear. Brush burgers with glaze during last several minutes of cooking.
Toast bread, if desired* (see note). Place a meat patty on each roll bottom, top with additional apple butter-ketchup glaze if desired, and the roll top.
*To toast the bread, spray the inside of bread with butter-flavored no-stick cooking spray. Place the bread (cut side down) around the outer edges of the cooking grate. Grill until golden brown.