Preheat oven to 400°F. Spray or brush a metal baking sheet (unlined so the fish will be crispy) with oil.
Season fish with salt and pepper; place into a bowl.
In a small bowl, combine dressing with herbs and mustard; coat fish on both sides.
In a second small bowl, combine pistachios, crumbs, and nutritional yeast, if using.
Place fish on the pan with the underside facing up.
Sprinkle with 1/3 of the crumble mixture.
Flip fish; thoroughly coat the top with remaining crumble so it looks nice and crusted.
Drizzle or spray fish with oil, then bake 20–25 minutes or to desired doneness.