Cut 8 (12x16") pieces of heavy-duty foil. Layer 2 pieces of foil on top of each other to create 4 stacks.
Place a flour tortilla in the center of each foil stack. Dividing evenly, top one half of each tortilla with chicken and cheese and season with salt and pepper. Fold tortillas in half, then bring edges of foil together to enclose the quesadillas and crimp edges to seal.
Prepare a campfire or grill for medium, indirect heat, preferably with hardwood or hardwood charcoal. Let coals burn until covered with ash and glowing red with no black remaining.
Place foil packs side by side directly onto hot coals or grill and cook, rotating with tongs occasionally, about 5 minutes. Carefully remove 1 packet from heat and check if cheese is melted. If necessary, return pack to coals and continue to cook, 5–10 minutes more. Serve with hot sauce, if desired.
