Place potatoes in a microwave safe bowl. Cover and microwave on high for 5 minutes. Stand, covered 5 minutes. Drain.
Meanwhile, make shallow cuts across chicken fillets, about 1½ cm apart. Combine oil, herbs, garlic, mustard and lemon juice in a large bowl. Add chicken and mix with clean hands to coat well.
Heat a large, lightly greased, flameproof roasting pan over a medium-high heat. Add chicken. Cook for about 2 minutes on each side, until lightly browned. Turn off heat. Transfer chicken to a plate. Add potatoes, onion, capsicum and zucchini to roasting pan. Toss gently. Arrange chicken over vegetables in pan.
Bake in a 220 °C oven (fan-forced) for 20 minutes. Remove. Add tomatoes and olives to pan. Bake for a further 10 minutes until chicken is cooked and vegetables are lightly browned and tender.
Meanwhile, place couscous in a heatproof bowl. Add ⅔ cup boiling water. Cover and stand 3 minutes, or until water is absorbed. Uncover. Fluff with a fork.
Serve roast with couscous and lemon wedges.