From http://www.recipegoldmine.com/grillveg/grillveg28.html

• Very large onions- sweet or Maui variety
• Brown sugar
• Beef bouillon cubes or granules

Slice onions in slices approximately 1/3 of an inch thick. Be careful to keep the onions together and not to separate the “rings.”

On a small square of aluminum foil, place onion slice, 1 heaping teaspoon of brown sugar, and 1 small beef bouillon cube. (If your cubes are larger, cut them in half). Fold the foil up tightly over the onion slice making sure to seal all of the edges . Throw them on your hot grill for approximately 20–30 minutes. The foil will puff up like Jiffy Pop! They should be cooked all of the way through, and have a wonderful caramelized appearance