Preheat oven to 325°F. Lightly coat both fish filets the olive oil. Season with salt and pepper.
In an oven-safe, nonstick pan over medium-high heat, sear the fillets skin-side down. When the skin is golden brown, transfer the pan to the oven and bake the fish for 7 minutes.
Peel sunchokes and onions, and boil separately until fork-tender. Puree the ingredients separately then mix them together, adding some of the cooking liquid to thin it out if needed.
Julienne a quarter of the apple and mix with salt, pepper, olive oil and lemon juice to taste.
To serve, add some the sunchoke-onion puree on the bottom of a plate and top with a fish filet and some of the apple salad.