Thai pumpkin soup

INGREDIENTS

• 1.5kg pumpkin or squash, peeled and roughly chopped
• 4 tsp sunflower oil
• 1 onion , sliced
• 1 tbsp grated ginger
• 1 lemongrass , bashed a little
• 3-4 tbsp Thai red curry paste
• 400ml can coconut milk
• 850ml vegetable stock
• lime juice and sugar, for seasoning
• 1 red chilli , sliced, to serve (optional)