Preheat oven to 425° F, dividing racks into upper and lower thirds. Line two large baking sheets with parchment. Combine mustard seed, coriander, a generous pinch of salt and pepper in a mortar; grind with a pestle to crack coriander seeds.
Place salmon on a baking sheet and rub with spice mixture, then 1 tablespoon olive oil. Roast salmon on upper rack until just cooked through, about 12 to 15 minutes total.
While salmon begins to roast, overlap sunchoke slices in small concentric circles on remaining prepared baking sheet, about 6 to 8 slices per galette. Drizzle galettes with 1 tablespoon oil and season with salt and pepper. Roast galettes on the bottom rack until crispy and browned, about 15 minutes.
While salmon and galettes roast, stir together remaining 2 tablespoons oil, lemon juice and mustard with parsley leaves; season with salt and pepper. Divide salmon into large pieces with two forks, and serve alongside galettes. Spoon vinaigrette over salmon.
Before her diagnosis, Caroline wrote a book on cakes called Cake Magic!. She started developing a birthday cake using her gluten-free mix found in that book. Check out other recipes she’s developing for her new life—and the stories behind them—on her blog, The Wright Recipes. Her next book, Catalan Food, written with chef Daniel Olivella, comes out in early September from Clarkson Potter.