- In a large pot of salted boiling water, cook the potatoes until tender. Drain. Keep warm.
- With the rack in the middle position, preheat the oven to 450 °F (230 °C).
- Meanwhile, in small bowl, combine the fennel leaves, tarragon and 2 tbsp (30 ml) of the green onions. Set aside.
- In a large baking dish, combine the zucchini, fennel, the remaining green onions and 2 tbsp (30 ml) of the olive oil. Season with salt and pepper. Bake for 20 minutes. Stir halfway through cooking.
- On a work surface, drizzle the remaining oil (1 tbsp / 15ml) over the fish fillets. Season with salt and pepper. Place the fish over the vegetables. Bake for about 10 minutes or until the fish is cooked through.
- Meanwhile, on a work surface, peel the grapefruit raw. Remove the grapefruit segments and cut into small pieces. Keep the juice. Spread the pieces of grapefruit over the fish and drizzle with the juice. Sprinkle the herb mixture over the vegetables, potatoes and fish.