Pumpkin and chickpea curry with peppers

1 tbsp sunflower oil

2 onions, finely chopped

2 green peppers, deseeded and cut into large chunks

1 red pepper,deseeded and cut into small chunky strips (optional for garnish)

3 large stalks lemongrass, bashed with the back of a knife

6 cardamom pods

3 tbsp Thai yellow curry paste

1 tbsp mustard seed

1 piece pumpkin or a small squash, peeled and roughly chopped

400ml can reduced-fat coconut milk

400g can chickpeas, drained and rinsed

2 limes

Large handful mint leaves

4 Naan breads, to serve