Season each fillet to taste with salt and pepper. Combine the potato and horseradish and spread the mixture over the top of each fillet, pressing it down so it will adhere.
Heat the oil in a large saute pan over medium heat until almost smoking. Sear each fillet potato-side down until a crust forms, about 3 minutes. Turn the fillets over and finish cooking in the oven until done, about 5 minutes for medium. Place on a large serving platter and top each fillet with some relish. Serve any remaining relish on the side.
Roasted Pepper Relish:
In a mixing bowl, combine the bell peppers, olives, pepper flakes, garlic, thyme, parsley, vinegar, honey, and oil. Season to taste with salt and pepper. May be refrigerated up to 1 day. Serve at room temperature.