Arrange the chicken pieces in a single layer in a roasting pan or baking dish and season generously with salt and pepper.
In a small bowl, zest both lemons, then halve and juice them into the bowl.
Add the olive oil, crushed garlic, mild chili powder and red chili flakes to the lemon juice and zest; whisk until well combined.
Brush the chicken pieces thoroughly with the marinade so they are evenly coated, then pour any remaining marinade over the pieces.
Cover the dish tightly with plastic wrap and refrigerate for 2 hours; do not marinate longer to avoid the acid breaking down the meat.
Preheat the oven to 375°F (190°C). Remove the plastic wrap and cover the roasting pan tightly with foil; cut a few small slits in the foil to vent.
Roast the chicken at 375°F for about 1 hour, until juices run clear and the internal temperature reaches 170°F (77°C).
Remove the foil, increase oven temperature to 425°F (220°C), and roast an additional ~10 minutes until the skin is nicely browned and crisp.