Line a baking sheet with foil and set a wire rack on top. Make 3 slashes across each chicken breast. Mix together the yogurt, garlic, ginger and tandoori paste and season well. Rub all over the chicken and leave to marinate for 5–10 minutes.
Toss the onion and chicken with the oil, then arrange on the rack. Place in a preheated oven, 230°C (450°F), Gas Mark 8, for 7 minutes.
Add the tomatoes, scatter over the butter and return to the oven for a further 5–10 minutes until the chicken is charred and just cooked through. Serve with lime wedges, raita and naan.