Position a rack in the center of the oven and heat the oven to 450ºF.
Combine the ginger, sesame seeds, coriander, cumin, fennel, red pepper flakes, and garlic in a food processor and process until the mixture is finely chopped, about 30 seconds. With the motor running, drizzle the oil through the feed tube and process, stopping to scrape down the sides, until the mixture forms a paste, about 20 seconds.
Rub oil on the salmon skin, and put the salmon, skin side down, on a rack set on a rimmed baking sheet. Sprinkle 2 tsp. salt evenly over the salmon. Using your hands, spread the spice paste onto the salmon. Roast until the salmon is cooked to your liking, 16 to 18 minutes for medium-rare.