Gather all of the ingredients.
In a large bowl combine ground meat.
Add onion, egg and seasonings.
Mix until well combined.
Use a kitchen scale to weigh out 5 oz balls from the meat mixture.
Form the balls into patties by hand or use a pattie press.
Place the patties on the smoker at 165 degrees F for two hours.
In a skillet, combine mushrooms and butter. Saute on medium heat until mushrooms are cooked (about 10 minutes).
Now place the patties on a grill preheated to 425 degrees F.
Cook for 8-10 minutes or until a meat thermometer inserted in the center reads 160 degrees F.
Flip half way through cooking and top each burger with a slice of Swiss cheese.
Serve each burger on a fresh hamburger bun with a generous serving of sauteed mushrooms.