Heat oven to 375°. In a large saucepan over medium heat, simmer parsnips in just enough water to cover; cook about 15 minutes. Let cool about 10 minutes. Remove parsnips from pan. Discard all but a quarter-cup cooking liquid and set aside. Slice parsnips into one-and-a-half-inch-thick strips and lay on a rimmed baking sheet, lightly oiled. Bake 20 to 25 minutes, or until nicely browned; turn parsnips at least once for even browning.
Using a food processor, pulse parsnips, lemon zest, and lemon juice together, until parsnips break down. With the motor running, add reserved parsnip liquid 1 tablespoon at a time, until mixture resembles loose apple butter. Pulse in olive oil and chopped chervil. Season to taste with salt and pepper. Keep warm.
Warm a large, dry saute pan over high heat. Brush each scallop on all sides with grapeseed oil and season with salt and pepper. Place scallops in hot pan, and don’t move them for 2 to 3 minutes, or until edges are well browned. Turn scallops over and cook 1 to 2 minutes longer. Place on a warm plate and let rest 2 minutes. Stir any juices that collect into parsnip puree.
Divide parsnip puree among 6 warmed appetizer plates. Set two scallops on top of puree and garnish with fresh chervil sprigs.