In a large no-stick frying pan over medium-high heat, combine the onions, vinegar, shallots, garlic, ginger, orange rind, and soy sauce. Bring to a boil, stir and cook for 30 seconds. Remove from heat. Add the cucumbers and pepper. Set aside.
Rub the salmon with olive oil and grill or broil for 4 to 5 minutes per side. Serve topped with the cucumber relish.