Whisk together mayonnaise, lemon juice, truffle oil, parsley, garlic, 1/4 teaspoon salt, and 1/8 teaspoon pepper in a small bowl.

Melt butter in a large cast-iron skillet over medium-high heat. Stir in mushrooms and thyme sprigs; cook, stirring occasionally, until mushrooms are tender and golden brown, about 10 minutes. Discard thyme sprigs. Season with 1/2 teaspoon salt and Worcestershire sauce. Transfer mushroom mixture to a bowl; keep warm for serving. Wipe out skillet.

Stir together garlic powder, onion powder, paprika, and remaining 1/2 teaspoon each salt and pepper for the rub. Divide beef into 4 portions; gently shape into balls.

Heat same skillet over medium-high heat. Working in batches as needed, add meat portions to dry skillet; press down firmly with a flat spatula or grill press into 41/2-inch-diameter patties. Sprinkle evenly with rub. Cook 2 minutes per side or until well browned. Top patties with Swiss cheese and cook about 30 seconds until cheese is melted and an instant- read thermometer inserted into centers registers at least 160 degrees F (71 degrees C).

To assemble burgers, spread bun tops and bottoms with truffle mayo. Fill buns with patties and sautéed mushrooms.