To make the marinade, mix the garlic, cumin, ground coriander, harissa paste, lemon juice, salt and pepper in a large bowl. Using a sharp knife, score each chicken breast diagonally 3 times. Add the chicken breasts to the bowl and rub well with the marinade. Cover with cling film and chill for 30 minutes.
Preheat the oven to 200 C / 180 C fan / Gas 6. Line a baking tray with foil. Place the chicken on the prepared baking tray, scored side up.
Bake in the preheated oven for 20 minutes or until the chicken is tender and cooked through (there should be no pink remaining).
While the chicken is cooking, deseed the peppers and cut into 3cm chunks. Cut the onion into 12 wedges. Trim the courgettes and cut diagonally into 1.5cm slices. Toss the vegetables with the olive oil, chilli flakes, sea salt and plenty of freshly ground black pepper.
Heat a large frying pan and add the vegetables. Stir fry over a medium heat for 6 minutes or until the vegetables are tender and lightly browned. Add the chickpeas and toss together for 1 to 2 minutes until hot.
Divide the vegetables and chickpeas between four warmed plates and top with the chicken. Drizzle over any juices and serve with spoonfuls of yoghurt. Garnish with roughly chopped flat leaf parsley or coriander if you like.