Soak plank in water 1 hour, then drain. Heat one side of grill to high heat.
Combine vinegar and next 7 ingredients in a large zip-top plastic bag; seal. Shake to combine. Add salmon; seal. Marinate in refrigerator 30 minutes, turning once.
Place wood plank on grill rack over high heat for 5 minutes or until lightly charred. Carefully turn plank over; move to cool side of grill. Remove fish from marinade; discard marinade.
Place fish, skin side down, on charred side of plank. Cover and grill 15 minutes or until fish flakes easily with fork. Sprinkle with onions and sesame seeds. Serve salmon on plank or carefully remove to serving dish.
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