Make the curry paste. Put the onions, chopped red chillies, garlic, ginger, lemongrass, lime zest and juice, and coriander stalks into a processor. Whizz to a paste, season, then whizz again with a little olive oil, to loosen as necessary.
Get a large pan nice and hot, and add the paste. Allow to cook down for a couple of minutes, stirring. Add the coconut milk and stir well. Bring to the boil, then reduce the heat to a simmer.
Add the prawns, red mullet and bream fillet pieces, cover with a lid and allow to simmer for 2–3 minutes. Next, add the mussels, cover with a lid, and cook for another 2–3 minutes, until all the shells are open. Discard any that remain shut.
Finish with a splash of soy sauce and serve on some cooked egg noodles. Scatter with the reserved coriander leaves and the sliced red chilli.