Heat olive oil in pan at medium high heat.
Add shallots, garlic and mushrooms, cook until tender, about 10 minutes.
Place in a bowl and add bread crumbs. Let cool for 15 minutes.
Add ground turkey, egg, dill, mustard, salt and pepper to the mushroom mixture and mix well until all ingredients are fully incorporated.
Form the mixture into 6 patties (1/2 inch thick)
Brush the patties generously with olive oil and cook patties for 5 minutes per side, on a grill at medium heat or in a nonstick grill pan.
Top each patty with 2 tbsp. of shredded Gruyere cheese and cook for an additional minute.
Lightly brush King’s Hawaiian Hawaiian Sweet Hamburger Buns with olive oil and grill 20 seconds on each side.
Place burger on bun and top with caramelized onions.
Melt butter and oil in a skillet over medium high heat.
Add onions to pan and stir to coat onions with butter and oil.
Cook for 30 – 40 minutes until onions are a deep brown. Stirring every 5 to 10 minutes.
Once onions are cooked add balsamic vinegar and cook for another 3 minutes and salt to taste.