You don't need an oven to make this chicken. Flattening the bird with a brick and cooking it in a skillet achieves a "roasted" finish.
Remove backbone from chicken using kitchen shears. Place chicken, breast side up, on a cutting board, with legs extended on both sides. Press firmly on breastbone to break it and flatten chicken. Rub all over with 2 tablespoons oil, and season generously with salt and pepper.
Heat 2 tablespoons oil in a cast-iron skillet set over a campfire or on a medium grill. Place chicken in skillet, breast side down, and place a clean brick or heavy skillet directly on top, pressing to flatten chicken. Grill until skin is golden and crisp, about 12 minutes.
Remove brick, and flip chicken. Cover with foil, and grill for 20 minutes more. Flip chicken, and grill until cooked through and an instant-read thermometer inserted into the thigh reaches 165 degrees, about 5 minutes more.
Meanwhile, grill lemon wedges directly on grates, flipping, until caramelized, about 2 minutes per side. Transfer chicken to a platter. Drizzle with remaining tablespoon oil, and sprinkle with red-pepper flakes. Serve with lemons.