Preheat oven to 450 degrees. Spread pine nuts on a rimmed baking sheet; toast in oven, tossing occasionally, until lightly golden, 5 to 7 minutes. Remove from sheet, and reserve. Meanwhile, place raisins and lemon zest in a small bowl; cover with boiling water. Set aside.
Place salmon fillets on the baking sheet used in step 1; season with salt and pepper. Roast until salmon is opaque throughout, 8 to 10 minutes.
Meanwhile, drain and discard liquid from raisins and lemon zest. Return raisins and zest to bowl; add lemon juice, pine nuts, parsley, and oil. Season with salt and pepper; stir to combine.
Dividing evenly, make a bed of spinach on each of four plates, place salmon fillet on spinach; spoon lemon relish over the top.