How to Make It
Preheat oven to 425°F. Toss cabbage wedges with 2 tablespoons of the oil on a rimmed baking sheet. Season with ½ teaspoon of the salt and ¼ teaspoon of the pepper. Roast until golden on the underside, 20 to 25 minutes.
Meanwhile, whisk together shallot, vinegar, mustard, and ¼ teaspoon each of the salt and pepper in a medium bowl. Slowly whisk in remaining 5 tablespoons oil until smooth and well-combined. Stir in olives and raisins; set aside.
Gently flip cabbage using a spatula, and move to one half of baking sheet. Carefully line other half of baking sheet with aluminum foil and lightly grease with oil. Arrange salmon on foil and season with remaining ¼ teaspoon each salt and pepper. Return baking sheet to oven and roast until salmon is just opaque, 10 to 14 minutes (depending on thickness).
To serve, place 1 salmon fillet and 2 cabbage wedges on each of 4 plates; spoon vinaigrette on top.