Drain the salmon, reserving 3/4 cup of the liquid. Flake the meat. Melt butter in a large frypan over medium-high heat. Add onion and cook until tender.
In a medium bowl, combine the onions with the reserved salmon liquid, 1/3 of the salada crumbs, eggs, parsley, mustard and salmon. Mix until well blended then shape into six patties. Coat patties in remaining salada crumbs.
Melt copha in a large frypan over medium heat. Cook patties until browned, then carefully turn and brown on the other side.