Prepare the mussels by scrubbing them under running water and pulling away the beard’ (the threads coming out of the side of the shell). Discard any that are cracked, or that are open and do not close when tapped on the side of the sink.
Pour the coconut milk into a large casserole that has a lid, and add the red onions, spring onions, garlic, chilli, lime zest and juice. Simmer over a gentle heat for 15 minutes.
Add the mussels to the casserole, put on the lid and allow to steam over a low heat for 5-8 minutes, giving them a shake or a stir a few times. Check the shells are open and the shellfish are cooked.
Spoon the mussels into 4 large bowls, discarding any that haven’t opened. Spoon over the liquor. Sprinkle with the fresh coriander leaves and serve with crusty bread, if you like.