Let the onion rest for 15min in water and salt to soften its flavour. Rinse and repeat 3 times.
Cut the fish in 2.5-3cm cubes. Any pieces that are too thin and might overcook go to the tiger's milk.
Mix the fish with the chili, onion, salt and pepper and let rest while we make the tiger's milk.
Squeeze the limes as close as you can to the moment of serving so they don't go bitter and keep them with an ice cube as you're squeezing them. Remove the ice cube for blending.
Put everything in the blender and pulse 3-6 times or until you see everything's now in small chunks.
Pass through a sieve and press down to really get all the juices.
Taste the tiger's milk and adjust the level of salt and also if it's too sour add sugar. You should be able to drink it and enjoy it on its own even without the fish.
Mix the tiger's milk with the fish and other ingredients and serve immediately.