Lightly season the fish on one side, then spread the tofu crab mousse evenly over the other side to form a coating. Place on a tray or plate, cover with plastic wrap and put in the fridge while you prepare everything else.
Put the lentils, leek, plantain, pandan leaf and ginger in a pan and add 500 ml water. Bring to the boil, stirring occasionally, and cook on a rapid simmer until the water has all but evaporated and the lentils are cooked and bursting. Add the black cardamom, coconut milk and another 200 ml water and simmer with a lid on for 20 minutes, stirring occasionally. Remove the pandan leaf and cardamom then mix in the tamarind and fish sauce. Pureée using a stick blender or bar blender and taste for seasoning. This can be made up to 3 days in advance if stored in the fridge once cooled.
Preheat the oven to 160°C. Place the panko crumbs onto a plate then press the mousse side of the fish into them gently to give an even coating. Place a frying-pan over a moderate heat and when it’s hot add vegetable oil to give a ½ cm depth. Place the fish in (as many portions as will fit comfortably), mousse-side down, and cook until the crumbs are a deep golden colour. Carefully flip the fish over and cook for 1 minute, then transfer to a baking tray (if your pan doesn’t hold all the fish at once). Place in the oven and cook for 3-5 minutes, depending on the thickness of your fish - to test if it’s cooked poke a small sharp knife into the thickest part - it should be translucent. Turn off the oven and open the door to keep it warm while you cook the vegetables.
While the fish is cooking, heat up a wok or a large wide pan or pot, and add a splash of vegetable oil. Add the Asian vegetables and toss or stir them for 30 seconds, keeping the wok on the heat. Mix the sesame oil, soy and mirin and add to the wok. The vegetables will only need a minute of cooking - you want them to stay crunchy.