Make the couscous by stirring the couscous, lemon zest and bouillon powder together and pouring over the olive oil and boiling water. Cover loosely with cling film and leave to stand for 10 minutes, fluffing up occasionally with a fork.
Meanwhile, make the lemon chicken by mixing the spring onions, tomatoes and harissa till blended. Stir in the chicken. Arrange the couscous and the chicken side by side on plates.