Preheat oven to 450F degrees.
Place raisins into a small sauce pan. Add enough water to cover raisins.
Over high heat bring to a boil, then reduce to simmer and cook for approximately 6-8 minutes until plump. Drain.
Transfer to blender and pulse untils mooth. Transfer to small bowl.
To raisin puree, add balsamic vinegar and garlic. Whisk to combine.
Line a baking sheet with aluminum foil or a silicone mat. Place salmon filet on baking sheet. Season with salt/pepper. Brush half of balsamic/raisin mixture onto salmon. Bake for approximately 10 minutes.
Brush with remaining balsamic/raisin mixture and return to oven for additional 5 minutes or until salmon flakeseasily with fork.
Garnish with onions if desired.