Place all the vegetables and tomatoes in a non-metallic bowl. Mix together the oil, lemon juice, garlic, ground spices and honey in a small bowl, then season and pour over the vegetables. Toss well and leave to marinate for 5 minutes.
To make the harissa yogurt, mix together the yogurt, garlic and harissa in a separate bowl, season and stir in the herbs, reserving some for garnish.
Using your hands, toss the vegetables and tomatoes gently in the marinade, then thread alternately onto 8 metal skewers. Cook over a barbecue or under a preheated grill, brushing with any remaining marinade, for 3–4 minutes on each side until browned and tender. Sprinkle with the reserved herbs and serve immediately with the harissa yogurt.