Peel and deseed the squash, then cut into bite sized chunks. Heat the oil in a large saucepan over a medium low heat. Add the onion and cook gently for about 10 minutes.
Add the garlic and chillies and cook for a couple more minutes then stir in the curry powder or paste and cook for a minute or two. Add the squash, season with salt and pepper and stir well to coat, then cook for a further 2 minutes.
Pour in the coconut milk, stir well and bring to a simmer. Cover and cook gently for 20-25 minutes stirring from time to time. You want the squash to be tender but not falling apart,and the cooking time will depend on the variety you have chosen.
When the squash is cooked to your liking check the seasoning then finish with a good squeeze of lemon or lime juice. Ladle into bowls and scatter with the coriander leaves then serve with rice and or naan or flatbreads.