In a skillet, heat the olive oil over medium heat. Add the chopped onions and sauté until translucent, about 3-4 minutes.

Stir in the minced garlic and chopped mushrooms. Cook for an additional 5-7 minutes, or until the mushrooms are tender and their moisture has evaporated. Remove from heat and let cool slightly.

In a large bowl, combine the ground beef (or plant-based alternative), sautéed mushroom mixture, Worcestershire sauce, salt, and black pepper. Mix until just combined; do not overmix.

Divide the mixture into 4 equal portions and shape them into burger patties.

Preheat a grill or skillet over medium-high heat. Cook the patties for about 4-5 minutes on each side, or until they reach your desired doneness.

In the last minute of cooking, top each patty with shredded Swiss cheese and cover to allow the cheese to melt.

Toast the hamburger buns lightly on the grill or in a toaster.

Place a lettuce leaf on the bottom half of each bun, followed by a burger patty with melted cheese, and top with tomato slices.

Add mayonnaise or your favorite sauce if desired, then cap with the top half of the bun.

Serve immediately while hot and enjoy your delicious Swiss mushroom burgers!