Heat oven to 190C/170C fan/gas 5. Score deep lines all over the chicken legs, then rub in the harissa. Season well and place in a roasting tin. Scatter the garlic over and around the chicken. Squeeze the lemon wedges over, then place them in the tin with the cherry tomatoes, potatoes and olives. Season, drizzle over the oil and toss briefly to mix everything together.
Cook in the oven for 45 mins-1 hr until the chicken is cooked through and golden. Serve with salad, if you like.