Put the potatoes in a pan of cold water, bring to the boil, then simmer for 8 minutes, until parboiled. Drain, cut in half and set aside. Preheat the grill or barbecue.
Meanwhile, heat half the oil in a pan and cook the onion and garlic for 5 minutes. Place in a bowl and let cool, then mix in the lamb mince, mint, egg yolk and breadcrumbs. Season with black pepper and mix well.
Roll into 16 balls and thread onto 8 metal or wooden skewers (soak wooden skewers in water for 30 minutes first), with the halloumi, courgette and potatoes.
Mix the remaining olive oil with the lemon zest and brush over the skewers. Cook on the barbecue or under a preheated grill for 15 minutes, turning once or twice, until golden and cooked through with no pink remaining.
Serve with the rocket salad and the tomatoes.