- Combine salt, granulated sugar, brown sugar, peppercorns, coriander seeds, fennel seeds, and red pepper flakes in medium bowl.
- Spread half of curing mix in center of foil-lined, rimmed baking sheet close to same size as fish. Place fish, skin side down, on curing mixture. Spread lemon zest, lime zest, and orange zest evenly over fish; cover with remaining curing mixture. Bring edges of foil up over salmon to enclose.
- Place second baking sheet on top of fish and weigh down with large cans. Refrigerate for 24 hours, unwrapping and flipping fish halfway through curing time.
- Unwrap fish and pat dry. Place on cutting board, skin side down Using long, sharp knife, cut fillets on diagonal, 1/8- to 1/4-inch thick, leaving skin behind. Wipe down blade with moist paper towel between each slice.
- Place slices on platter, cover tightly, and chill until ready to serve.
- Salmon may be cured 3 days ahead. Serve with bagels and cream cheese, sliced cucumbers, or tossed green salad.
Beverage pairing: Pale ale, Champagne, or Prosecco