Char-grilled lamb with tomato chickpeas

Ingredients

• 1 tablespoon olive oil
• 1 medium (170g) red onion, cut into thin wedges
• 2 cloves garlic, crushed
• 400 grams can chickpeas, drained, rinsed
• 400 grams can chopped tomatoes
• 2 teaspoons tomato paste
• 1 teaspoon sugar
• 1 lemon, rind finely grated, juiced
• 1 1/2 teaspoon ground cumin
• 1 teaspoon ground cinnamon 500g lamb back strap (eye of loin) or fillet
• olive oil cooking spray
• 1/2 cup coarsely chopped fresh mint leaves
• 200g steamed green beans, to serve