Over high heat, put the water in a pot, bring to a boil. and add the salt and shells from the shrimp. Reduce to a simmer and let it cook for 15minutes. Strain the mix and put it back in the pot. Bring it back to a boil and add the peppers, mushrooms, lemongrass, zest, fish sauce, and shrimps. Let it simmer for about 5 minutes. Add half the lime juice, do a taste test, adjust with either more lime juice or more fish sauce depending on how you like it.

Remove lemongrass sticks and serve. At this point, you can add the coriander to your bowl to decorate