In this recipe, the onions and potatoes are double-wrapped in foil to prevent the flavorful juices from leaking out when the packet is flipped during grilling.
Wash and dry potatoes. Quarter round red potatoes, if using. Cut any larger fingerling potatoes in half lengthwise, if using. Place a 24x18-inch sheet of heavy foil on a flat surface. Place potatoes and onions on foil. Drizzle with olive oil; sprinkle with salt, chili powder, and pepper (see Tip). Bring up two opposite edges of foil; seal with a double fold. Fold remaining ends to completely enclose the potatoes, leaving space for steam to build. Wrap with a second 24x18-inch piece of heavy foil to insulate.
Place foil-wrapped potatoes directly on medium-low coals. Grill about 40 minutes or until potatoes are tender, turning packet halfway through grilling. (Or place packet on a grill rack over medium coals and grill for 45 to 60 minutes or until potatoes are tender, turning packet every 20 minutes.) Serve warm.
Tip: Combine seasonings in a small plastic bag to carry to the campsite.
1 1/2 starch