Pat the chicken dry, remove the gizzards (if applicable), and let it sit out of the fridge for 1 ½ hours. Remove the backbone, flip breast side down, and push firmly to crack the bone and open it flat. Pat dry again.
Heat the BBQ to maximum. Toss the chillies with olive oil and salt, grill 10-12 minutes until charred and soft, then cool.
Deseed the chillies if you want it milder, then blend with the remaining harissa ingredients (except the butter) to a thick paste. Season to taste.
Rub the chicken with half the harissa, working some under the skin, then drizzle with the reserved oil and season. Grill breast side up 10 minutes, flip 5 minutes, then move to indirect heat with the lid down for 35-40 minutes until it hits 70°C (158°F) internally. Rest 5-10 minutes, tented loosely in foil.
Melt the remaining harissa paste with the butter in a saucepan to make the sauce, season, and set aside.
Whisk together the spiced yogurt ingredients, season, and refrigerate until serving.
Spread the yogurt on a platter, top with the chicken, drizzle with the harissa butter sauce, and garnish with coriander and lime wedges.
Chef's Tips
Letting the chicken come to room temperature before grilling matters; a cold chicken cooks unevenly and risks drying out before the centre's done.Direct heat first, then indirect with the lid down, gets a properly charred skin without burning the harissa's sugars before the inside's cooked through.Resting 5-10 minutes lets the juices redistribute instead of spilling out the moment you cut in.
Storage & Reheating
Best served fresh off the grill. Leftovers keep in the fridge up to 3 days, reheated gently in a low oven.