Slice potatoes and onion into 1/8 - 1/4" slices.

Place on piece of aluminum foil large enough to fold over and to be able to roll up edges.

Top with garlic, butter, Worchestershire and cayenne.

Fold packet over and roll edges to close.

Leave on medium grill for 30 minutes or in 350 oven (in a pan to avoid messes) for 35-40 minutes.