In a skillet, melt the butter over medium heat. Add the sliced mushrooms and sauté for about 5-7 minutes, until they are golden brown and tender.
Add the minced garlic, salt, and pepper. Cook for an additional 1-2 minutes until fragrant. Remove from heat and stir in fresh parsley if using.
Make the Burger Patties:
In a mixing bowl, combine the ground beef, garlic powder, onion powder, salt, and pepper. Mix until just combined.
Divide the mixture into 4 equal portions and shape them into patties, making a slight indentation in the center to help them cook evenly.
Cook the Burgers:
Preheat a grill or skillet over medium-high heat. Cook the burger patties for about 4-5 minutes on each side, or until they reach your desired doneness.
In the last minute of cooking, place a slice of Swiss cheese on each patty and cover to melt the cheese.
Assemble the Burgers:
Toast the burger buns if desired. Place a lettuce leaf on the bottom half of each bun, followed by the cheese-topped burger patty and a generous spoonful of sautéed mushrooms. Add tomato and pickles if desired, then top with the other half of the bun.
Serve:
Serve your Swiss Mushroom Burgers immediately with your favorite sides, such as fries or a side salad.