Preheat the oven to 200°C/gas mark 6.
Heat the oil in a non-stick pan, add the chicken and fry for 2 minutes on each side until browned.
Place the couscous in an ovenproof dish. Mix together with the stock, red onion, red pepper, parsley and the lemon zest and juice, then pour over the couscous and stir.
Place the chicken on top of the couscous, then spoon over the pesto and season to taste.
Cover the dish with foil and bake for 20 minutes.
Once cooked, fluff up the couscous with a fork. Serve hot or cold.