In a skillet, melt 1 tablespoon butter and add mushrooms and garlic salt. Sauté until mushrooms are browned and tender, about 2–3 minutes. Cover and set mushrooms aside. Butter one side of each bun and cook face down on skillet for 1 minute or until bun is toasted. Season burgers generously with salt, pepper, and Worcestershire sauce. Add to medium heat skillet and cook 3–5 minutes. Flip burgers and add cheese.
Cover and cook another 3–5 minutes. Assemble each burger with buns, lettuce, tomato, burger, and mushrooms.
Add condiments as desired.