Preparation: Cut beef into 1 inch cubes. Grate onion inside gallon size zip-lock bag to save onion juice. Place beef chunks into bag with grated onion, pour lemon juice over beef. Seal bag and mix together to ensure even coverage. Place bag inside a large bowl and refrigerate overnight or up to 3 days (the longer the better, in my opinion).
Cooking: drain juice from beef and onion and thread beef chunks onto metal or water soaked bamboo skewers. Place under broiler (with oven rack on the second from the top brackets) for 10-20 minutes or until edges are dark brown and crispy, turning every 5 minutes or so. Meat can also be cooked on a hibachi or regular grill. Meat does not need to be cooked to 160 degrees (and should not be!) as the lemon juice “cooks” the meat with enzymes while it marinates.