Mix the harissa with half the mint and rub into the lamb.
Heat a large griddle pan over a medium heat and lightly brush with the olive oil. Add the lamb and cook for 10 minutes for medium rare (cook for 2 minutes longer if you prefer medium). Turn occasionally, but allow the meat to char.
Meanwhile, put the couscous in a bowl and pour over 250ml boiling water. Cover with clingfilm and set aside for 5 minutes. Fluff up with a fork and stir in the chickpeas, onion and remaining mint. Drizzle the dressing over the top and mix well.
Divide the couscous between 4 plates and top with the spinach. Slice the lamb, place it on top of the salad and serve.