- Preheat grill to medium-high heat.
- In a medium bowl combine the ground beef, salt, pepper, garlic powder and Worcestershire sauce.
- Use your hands to form four ½-inch thick patties. Place on a plate in the fridge until ready to grill.
- Melt the butter in a cast iron skillet placed on a stove set to medium heat.
- Add the onions, sugar, salt and pepper. Cook, stirring occasionally for 5-6 minutes, or until light brown and soft.
- Add sliced mushrooms and continue to cook for another 5-6 minutes or until onions have caramelized and mushrooms are soft. Add garlic and parsley and cook until fragrant. Place in a bowl and cover with foil to keep warm.
- Place patties on preheated grill. Grill patties over direct heat until cooked to desired doneness (5-8 minutes) flipping halfway through.
- During the last minute of grilling time, place one slice of Tillamook Swiss Cheese slice on each patty and place the buns cut side down to toast. Close lid of grill until cheese has melted. Remove from grill.
- When ready to assemble, place the burger patty on the buns, top with the
caramelized onion mixture, lettuce, and any other toppings you might want.