Spray a large saucepan with low-calorie cooking spray and set over a medium heat.
Add the onions and peppers and sauté for 5 minutes until beginning to soften.
Add the garlic and ginger and stir well.
Add the cumin, ground coriander and chilli flakes and cook for 1 minute until the spices become aromatic.
Stir in the lemongrass paste and tomato puree, then add the stock and coconut milk and butternut squash.
Bring to a boil, then reduce the heat to a simmer. Allow to cook for 35 minutes until the butternut squash is soft.
Add the lime juice and soy sauce.
Blitz the soup using a food processor or stick blender. Take care not to splash yourself with hot soup!
Return to the pan and make sure it is piping hot. Stir in the chopped coriander and serve.