Thaw salmon, if frozen. Cut salmon fillets into eight equal pieces. Brush the unheated rack of a broiler pan with oil and arrange salmon on the rack. Broil 4 inches form the heat until fish flakes easily when tested with a fork, allowing 4 to 6 minutes for each 1/2 inch of thickness.
For sauce, stir together yogurt; lemon juice; horseradish; fennel tops, if desired; and pepper in a small mixing bowl. To serve, place salmon on Lentil Pilaf and drizzle with yogurt sauce. Garnish with fennel leaves, if desired. Makes 8 servings.