With the rack in the highest position, preheat the oven’s broiler. Line a baking sheet with aluminum foil.
In a bowl, combine the oil, lemon juice, mustard, and garlic with a whisk. Keep the vinaigrette aside.
In a bowl, toss the cauliflower with half the vinaigrette. Season with salt and pepper. Place on the baking sheet. Bake for about 10 minutes. Remove from the oven. Toss the cauliflower and add the fish on the side. Brush the fish with the mustard. Season with salt and pepper. Bake for about 6 minutes or until the fish is cooked, depending on its thickness.
Meanwhile, combine the remaining vinaigrette with the pistachios, tomatoes, and olives. Serve over the fish.
Recipes with the "Healthy Pick" stamp have been evaluated by a registered dietitian member of the Ordre professionnel des diététistes du Québec.