Cut your mushrooms into bite-sized pieces and place them into a pot of boiling water. Allow them to cook through, approximately 5 minutes. Remove them from the water and let cool to room temperature while preparing the rest of the salad.
Slice the shallots and the bottom tender part of the lemongrass very finely. Remove the mint leaves from their stems. Slice the Thai chili into small pieces.
Make the dressing by mixing the lime juice, fish sauce, and palm sugar. Taste and adjust as necessary, depending on the sourness of your limes.
Combine the sliced herbs and dressing with the mushrooms. Mix everything together and do one more taste test, again adjusting according to your personal preferences. Enjoy immediately!