Preheat the oven to 350 degrees F. With kitchen shears or a knife, cut along either side of the chicken's backbone and remove it. Place the chicken, skin-side down, on a cutting board and firmly press it flat. Set the chicken, skin side up in a roasting pan.
Combine the oil, garlic, lemon zest and juice, oregano, paprika, cumin and cayenne in a small bowl. Brush all over the chicken; season with salt and pepper.
Roast the chicken, basting occasionally, for 75 to 80 minutes, or until a meat thermometer inserted into the centre of a thigh registers 170 degrees F. Let the chicken rest a few minutes before carving.