Preheat the oven to 200 degrees Celsius. Clean the Brussels sprouts by trimming the tough bottoms and removing the outer leaves. Cut the pumpkin into equal chunks. Cut the lemon in half, squeeze one half and cut the other half into small wedges.
Place the wild salmon and cleaned Brussels sprouts side by side on a baking sheet lined with parchment paper. Drizzle the fresh lemon juice over the fish and vegetables and season with salt and pepper to taste. Roast everything in the preheated oven for about fifteen minutes until cooked through.
Meanwhile, cook the pumpkin chunks in a pan with plenty of water for ten to twelve minutes until completely tender. Drain the cooking liquid and let the vegetable steam dry briefly. Then mash the pumpkin pieces vigorously together until you achieve a smooth puree.
Spread the warm pumpkin puree evenly across the plates. Place the roasted wild salmon in the center on top. Arrange the warm Brussels sprouts around the fish and serve immediately with the remaining lemon wedges on the side.