Make 1 cm deep cuts, about 2 cm apart, diagonally across the top of chicken fillets. Place chicken in a single layer in a shallow dish.
Combine tandoori paste with 2 tablespoons of the yoghurt in a small bowl (reserve remaining yoghurt to serve). Rub tandoori mixture all over chicken. Cover and set aside in the fridge.
Place sweet potato, cauliflower and onion on a large, shallow-sided baking tray. Drizzle with half the oil, toss well and spread in an even layer. Bake in a 220 °C preheated oven for 20 minutes.
Remove tray from oven and turn vegetables. Add zucchini and capsicum to tray. Place chicken amongst vegetables so it’s resting on the hot tray. Drizzle over remaining oil. Return to oven. Bake at 220 °C for a further 20-25 minutes, until vegetables are browned and tender, and chicken is cooked through.
Meanwhile, mix reserved yoghurt with about 1 tablespoon cold water to thin to a drizzling consistency.
To serve, drizzle yoghurt over chicken and vegetables. Sprinkle with mint leaves. Serve with lemon wedges.