How to Make It
In a medium skillet, toast the poppy seeds over high heat, stirring, until they smell slightly nutty, about 2 minutes.
In a heatproof bowl, cover the hibiscus flowers with the boiling water and let steep for 1 hour. Strain into a bowl.
Add the mezcal to the hibiscus liquid along with the salt, brown sugar and grapefruit and lime zests. Put the snapper fillets in a large, resealable plastic bag and add the hibiscus liquid. Refrigerate, turning the fish often, until red and lightly cured, about 45 minutes.
Meanwhile, scoop the passion fruit pulp and seeds into a large bowl and add the lime juice, shallot and fish sauce. Add the cucumbers and cilantro to the bowl and toss well.
Using a sharp knife, thinly slice the fillets and fan the slices out on plates. Arrange the cucumber salad alongside. Sprinkle the salad with the toasted poppy seeds and serve.
Dried hibiscus flowers are available at health food stores, Latin markets and tea shops. The color of a passion fruit's skin is not indicative of its ripeness. Whether green or purple, look for thin-skinned fruits with plenty of wrinkles. Passion fruits with smooth, thick skins are underripe.