1 large sweet onion, such as Vidalia, thinly sliced
1 tablespoon packed brown sugar
1 tablespoon olive oil
1 tablespoon McCormick® Grill Mates® Steakhouse Onion Burger Seasoning
1 pound ground beef
2 tablespoons ketchup
4 slices American or Cheddar cheese
4 hamburger rolls
Toss onion, brown sugar, oil and 1 teaspoon of the seasoning in large bowl until well blended. Spoon onto center of double layer sheet of aluminum foil. Bring up sides of foil; double fold top and ends to tightly seal packet.
Mix ground beef, ketchup and remaining 1 tablespoon seasoning in large bowl until well blended. Shape into 4 patties.
Grill foil packet over medium heat 20 minutes or until onions are tender, turning packet over halfway through cook time. Grill burgers over medium heat 4 to 6 minutes per side or until cooked through (internal temperature of 160°F). Add cheese slices to burgers 1 minute before cooking is completed. Toast rolls on the grill, open-side down, about 30 seconds or until golden.
Serve burgers on toasted rolls with caramelized onions. Garnish with desired toppings and condiments.