Thaw the tilapia fillet in the refrigerator the day before you prepare it. Do this on a rack so it can release water while it defrosts.
Cut into strips like fajitas.
Using a molcajete or mortar, crush and blend the garlic and achiote while adding lemon juice. Marinate the fish in this mixture for an hour in the refrigerator.
Cut the red onion in brunoise, like the coriander, and mix with the frozen mango. Leave the mixture to marinate.
Crumble the fresh cheese into small irregular pieces.