Mix the sliced apple with the lemon juice to stop it going brown. Put the couscous and peas in a heatproof bowl. Pour over 200ml boiling water, cover and let sit for 5 minutes, until the water has been absorbed.
Fluff up the couscous with a fork, then stir in 2 tablespoons of the harissa paste. Add three-quarters of the apple, along with the mint leaves and mix well. In a separate bowl, combine the chicken with the remaining 1 tablespoon harissa paste.
Divide the couscous mixture among 4 serving plates and top with the harissa chicken. Scatter over the remaining apple slices and crumble over the goats’ cheese. Garnish with extra mint leaves to serve.