Clean and cut the fish into large pieces. In a pot, add water, fish, lemongrass, half of the onions, garlic, ginger, fish sauce, and tamarind paste. Bring to a boil and then simmer for about 20 minutes.

Remove the fish and set aside to cool. Strain the broth and discard the solids.

Heat oil in a pan and stir in the remaining onions and garlic until fragrant. Add paprika powder, chili powder, and chickpea flour or cornstarch, and stir until combined.

Slowly pour the fish broth into the pan and stir continuously until the mixture thickens.

Break the cooled fish into small pieces and add them into the broth.

Cook the rice noodles according to packet instructions.

To serve, place a serving of noodles in a bowl and pour the fish broth over the noodles. Add the garnishes on top.