Pumpkin curry with chickpeas

INGREDIENTS

• 1 tbsp sunflower oil
• 3 tbsp Thai yellow curry paste
• 2 onions , finely chopped
• 3 large stalks lemongrass , bashed with the back of a knife
• 6 cardamom pods
• 1 tbsp mustard seed
• 1 piece pumpkin or a small squash (about 1kg)
• 250ml vegetable stock
• 400ml can reduced-fat coconut milk
• 400g can chickpeas , drained and rinsed
• 2 limes
• large handful mint leaves
• naan bread , to serve