Slice Lions Mane mushroom into 2 thick slices, approx. ½ inch thick apiece. Reserve remaining mushroom.
Chop trumpet mushroom and reserved lions mane.
Preheat cast iron pan over med/high heat.
Add ½ tbs butter and saute diced mushrooms till lightly browned. Add salt and pepper to taste. Set aside and wipe out pan with paper towel.
Using the same pan, add butter and lions mane shrooms. Cook till golden brown on both sides about 3 minutes per side.
Lower heat to medium and top each mushroom with 2 slices of Swiss each.
Slice buns in half and place a mushroom burger on each. Top with sautéed mushrooms and top with bun. Enjoy!