For the relish:
In a medium bowl, whisk together all the relish ingredients except the cucumber.
Add the cucumber, stir well and allow to stand at room temperature for at least 15 minutes.
Lightly brush or spray the salmon all over with oil.
Season with pepper to taste.
Barbeque the salmon for 4 to 5 minutes each side or until opaque throughout.
Serve with the relish spooned over the top.