Cook quinoa per pkg. directions. Meanwhile, in a small bowl, combine lemon juice, mustard, 2 Tbsp oil, and 1/2 tsp salt. Heat a large skillet on medium. Pat salmon dry, season with 1/4 tsp salt, then press one side of each fillet in sesame seeds, pressing to coat. Add remaining Tbsp olive oil to the skillet, then salmon, coated side down, and sear until golden brown, about 6 minutes. Flip and cook until browned and cooked through, about 4 minutes. Fluff quinoa with a fork and add spinach and lemon zest. Stir pistachios into vinaigrette. Serve quinoa with fish and drizzle with pistachio vinaigrette.