Begin by placing your ground beef in a large bowl.
Mix together Guinness, Worcestershire, minced onion, and garlic powder in a small bowl.
Pour over the top of the beef, and incorporate well into the meat. There will be plenty of liquid.
Marinate for at least 1 hour, up to 8 hours in the fridge.
Heat up your grill.
Divide the meat into 6 portions, and form each portion into a ball. Flatten into a patty about 1/2-1 inch thick.
Grill each patty for approximately 5 minutes each side (for medium-medium well burgers).
Top with cheddar and any other additional garnishes.