Sautéed mushrooms and onion with a little Swiss cheese are stuffed in hamburger patties to create an exciting twist on a classic flavor combination.
Heat butter in nonstick skillet over medium heat. Add mushrooms and onion; cook and stir 4 minutes or until mushrooms have softened. Cool completely.
Mix ground beef and steak seasoning. Measure 12 (1/4-cup) portions of beef. Shape into thin 4-inch round patties. Place about 1 tablespoon each of the mushroom mixture and cheese in center of each of 6 patties. Top with remaining hamburger patties, pinching edges to seal filling. If necessary, lightly flatten with spatula.
Grill over medium heat 4 to 6 minutes per side or until burgers are cooked through.
Serve burgers on toasted rolls. Garnish with desired condiments and toppings.