Taima's easy BBQ potatoes

This recipe is from Carmelle and Yvon on s/v Taima.
Instead of baking potatoes whole on the BBQ (which takes forever!), try this method:

3 potatoes, peeled and sliced.
1 onion, peeled and sliced
salt
pepper
olive oil

Place the potatos and onion in alternating layers on a piece of aluminum foil. Cover liberally with olive oil, salt and pepper. Seal up the package and BBQ on low heat for about 20 minutes or so.