With the rack in the middle position, preheat the oven to 425°F (210°C).
On a baking sheet, without parchment paper or silicone mat, toss to coat the bell peppers and onion with the oil. Bake for 15 minutes.
Cut the Brussels sprouts in half and spread them onto the baking sheet with the peppers. Place the trout fillets in the centre of the vegetables. Season with salt and pepper. Bake for 10 minutes or until the fish is cooked and breaks apart easily with a fork. Sprinkle with 2 tbsp (30 ml) of the basil.
In a bowl, combine the mayonnaise, water and the remaining basil (2 tbsp/30 ml). Serve with the trout and vegetables.
Recipes with the "Healthy Pick" stamp have been evaluated by a registered dietitian member of the Ordre professionnel des diététistes du Québec.