This is a dish that can be changed or adapted according to whatever is fresh in the seafood market. You can substitute or add langoustines or crayfish, sea snails, small whole fresh fish or skin-on fish fillets, or whatever else you like. Just make sure the pan you use is large enough so the seafood is laid out in one layer. If you don't have one that is large enough, use two, dividing the seafood between them.
Keto diet followers need to omit the banana chillies and spring onions, and go light on the salsa verde.
Make the salsa verde. Put the fresh coriander, garlic, citrus zest and fish sauce in a food processor blender or immersion blender and process to a rough purée. With the motor running, add the calamansi or lime juice and the olive oil through the feed tube. The purée should have some texture; don't make it too smooth. Taste for seasonings and correct, if necessary. If it's too thick, stir in more olive oil. Transfer the mixture to a serving bowl and set it aside.
Preheat the oven to 250°C (480°F).
Clean the calamari. Pull the tentacles and face from the body. From the body, remove the innards and quill, then take off the purplish skin. Discard the innards, skin and face of the calamari, reserving the tentacles and bodies.
Prepare the razor clams. Detach the meat from the shells then trim off the stomach and other inedible parts. Break off and discard the top shell, then lay the clam meat back in the other shell.
Mince the garlic.
Pour about 60ml (4tbsp) of olive oil into the pan, adding more if necessary to coat it lightly. Set it over your largest burner with the flame on high. Add the banana chillies and cook them on all sides until the skin blisters, then remove from the pan. Cook the spring onions the same way.
Turn the flame to medium then add the prawns and cook them for about one minute on each side. Remove them from the pan. Lightly sear the calamari bodies on both sides, then remove from the pan.
Add more olive oil to the pan so it is well coated, then sprinkle with a very light, even layer of salt. Arrange the prawns and calamari (bodies and tentacles) in the pan, then add the remaining seafood. Drizzle with more olive oil then sprinkle very lightly with salt. Scatter the garlic on top. Put the pan in the oven and cook for four minutes. Quickly arrange the chillies on top then continue to cook for about two more minutes, or until the clams and mussels have opened.
Spoon some of the salsa verde over the seafood then drape the spring onions on top. Serve immediately, with the remaining salsa verde on the side.