Preheat oven to 375º.
Combine potato, horseradish, 1/4 teaspoon salt, and pepper. Sprinkle both sides of fillets with 1/4 teaspoon salt. Spread 1/4 cup potato mixture over 1 side of each fillet, pressing potato mixture onto fish. Heat 2 teaspoons olive oil in a large nonstick skillet over medium-high heat. Add 2 fillets, potato side down, to pan. Cook 3 minutes or until potato mixture is browned. Carefully turn fish over; place on a plate. Repeat procedure with remaining oil and fish. Return fish to pan, potato side up. Bake at 375º for 5 minutes or until fish flakes easily when tested with a fork. Serve with lemon wedges.