Bring a small pot of water to a boil. Add potatoes and boil until just starting to get tender, 15-20 minutes. Remove from water and let cool slightly then cut into wedges.
Spread out foil pieces and drizzle with 1 teaspoon of oil each.
Add the remaining ingredients, splitting them between the two pieces of foil, drizzling with however much BBQ sauce you prefer (a tablespoon or so each should be enough). Also add half of the potatoes to each.
Seal foil into tight packets and place on a grill over indirect heat for about 10-15 minutes or until the onion has started to soften.
Remove from grill and open to let cool before serving.
Notes
If you aren't careful the bottoms of the packets can get very hot. Let them cool before serving!