Form beef into eight loose patties; season with 3/4 teaspoon salt and black pepper.

Heat half the oil in a skillet. Cook mushrooms with remaining salt for 7 minutes until browned and dry.

Transfer mushrooms to a plate. Add remaining oil; cook patties 3 minutes per side until 160°F.

Top each patty with mushrooms and half a Swiss slice.

Cover 30 seconds until cheese softens.

Place patties in buns; serve hot.