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.
Meanwhile, make the chimichurri sauce by combining parsley, olive oil, red wine vinegar, garlic cloves, oregano and salt & pepper in a food processor.
Now turn the grill up to 425 degrees F.
Cook the patties 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 cheese.
Serve each burger on a brioche hamburger bun with a generous serving of the chimichurri sauce.