To prepare the relish, combine the first 8 ingredients, stirring well. Cover and chill.
To prepare salmon, combine 1 cup onion and next 5 ingredients (onion through bay leaf) in a Dutch oven; bring to a simmer. Cover and cook 20 minutes. Strain liquid through a sieve into a bowl; discard solids.
Return liquid to pan; bring to a simmer. Add salmon; cover and cook 5 minutes. Remove from heat; let stand 5 minutes. Remove salmon from pan; chill. Discard cooking liquid. Serve relish over salmon.