In a large piece of aluminum foil, place onions on the bottom, top with potatoes, ghee & seasonings. Bring edges of foil together to enclose the package, covering completely, then crimp to seal package closed.
Heat grill to medium heat (around 400°) Place foil packages near the part of the grill with the least indirect heat and cook, moving package around occasionally for even cooking, until potatoes are tender, 30–45 minutes.
Remove from grill, allow to cook for a couple of minutes before opening the foil. Be mindful of steam! Toss the potatoes and onions then serve.