Combine stock concentrate and hot water.
In a large flat-based pot over low heat, add oil, onion, garlic, chilli and ginger and gently cook for 3 minutes. Increase heat to medium-high then add mussels and stock. Cover pot with lid and cook for 6 minutes or until mussels just start to open (discard any that don’t open). Remove from heat and leave mussels to cool.
When cool enough to handle, remove tongues and beards (see below) then separate mussel meat from shells. Transfer to a large serving bowl to keep warm.
In the same pot over medium heat, add coconut milk and cook until reduced by half (around 10 minutes) then stir in lime juice.
Place mussel meat back in the shells then pour the sauce over. Finish with a sprinkling of coriander and serve with lime wedges on the side.