Warm the oil in a saucepan over a medium heat. Add the onion and cook and stir until soft. Add the celery, ginger and crushed garlic and continue cooking until all the ingredients are soft.
Add the Thai red curry paste and cook for a few minutes to allow the flavours to develop. Add the diced squash and pour over the vegetable stock. Add the kaffir lime leaf and bring to the boil. Reduce the heat and simmer until the squash is tender, around 15 minutes.
Remove the lime leaf, add coconut milk and heat through. Using a handheld liquidiser or food processor, blend until smooth - you can add more stock if the consistency is too thick; season well. Ladle into warmed bowls and garnish with chopped green chilli and fresh coriander. Serve.