Mix together the ground beef, onion, mushrooms, garlic, egg white, and seasoned salt in a bowl. Form six equal-sized hamburger patties from the mixture. Season burgers on each side with salt and pepper.
Heat a large skillet over medium-high heat. Lie the patties into the skillet and cook until golden brown, about 3 minutes per side. Top each with a slice of Swiss cheese shortly before removing the burgers from the skillet; serve on hamburger buns.
