
Place the broth, ginger, zest, salt, and pepper flakes in a 4-quart or larger saucepan or pot over medium heat and bring to a boil. Cover and simmer for 5 minutes for the flavors to infuse.
Add the coconut milk, fish sauce, and sugar, and bring back to a simmer uncovered. Add the dumplings, mushrooms, and snow peas, and simmer, stirring occasionally, until the dumplings are cooked through according to package directions.
Remove from the heat and stir in the lime juice. Taste and season with more salt, fish sauce, pepper flakes, or lime juice as needed. Serve immediately, garnished with cilantro if desired.