Combine cheese, margarine, mayonnaise, green onions and chives in a small bowl and stir well. Set aside.
Place fillets on a lightly greased rack in a broiler pan. Dizzle lemon juice over fillets; sprinkle with pepper. Broil 6 inches from heat 8 to 10 minutes or until fish flakes easily when tested with a fork.
Remove from oven and spread tops of fillets with cheese mixture. Broil an additional 2 minutes or until cheese is lightly browned and bubbly.
Remove fillets to a serving platter. If desired, garnish with lemon slices and fresh chives.