Position a rack in the center of the oven and heat the oven to 400ºF.
In a small bowl, combine the shallot, vinegar, lemon juice, orange juice, lemon zest, orange zest, and a pinch of salt. Let the mixture sit for 5 to 10 minutes.
Meanwhile, season the salmon with salt, put it on an oiled rimmed baking sheet, and drizzle a thin stream of oil on top. Bake until it’s done to your liking, about 6 minutes for medium, 8 minutes for medium well, keeping in mind that it will continue to cook after it comes out of the oven.
Whisk the 1/4 cup oil into the shallot mixture, taste, and adjust the seasoning with a drop of vinegar if necessary. Transfer the salmon to four dinner plates, spoon about 2 Tbs. of the vinaigrette onto each portion, sprinkle the chervil leaves or cilantro on top, and serve.