Place the mahi-mahi in a medium bowl and sprinkle with the sea salt. Line a plate with a brown paper bag. Set aside.
In a small skillet over medium-high heat, warm the vegetable oil until it’s hot but not sizzling. Add the ancho and fry for about 1 minute. Transfer the chile to the prepared plate to drain.
Using the same pan and hot oil, fry the hibiscus flowers until crisp, then place them on the plate to drain.
When the chile and hibiscus are cool enough to handle, place them on a cutting board and chop them together until you have a deep red crumble of little bits and set aside.
To the bowl with the mahi-mahi, add the lime juice, olive oil, chives, and chile-hibiscus mixture and toss to combine. Add the avocado and finishing salt. Serve immediately.
Ceviche is at its prime the day it is made, so don’t make more than you intend to serve and eat.