Fillet the trout and remove skin with a sharp knife, then combine the cure mix by hand - salt, sugar, coriander seeds, peppercorns, zest and chopped fennel.
Dust cure mix in tray. Lay the side of trout on top of cure mix, then cover with rest of the cure mix and cure in the fridge for 2 hours, based on a 2 kg whole fish (add 1 hour per kg if required, or if using Norwegian/Scottish/Chilean salmon as a substitute). Then rinse under cool running water and dab dry. Store covered in the fridge.
Do the curing process first, then follow the garnish steps accordingly so as to have correct timing on completion.