1. Prepare Greek Tapenade; set aside.
2. Sprinkle fillets evenly with salt and pepper. Heat a large nonstick over medium-high heat; coat pan with cooking spray. Add fish; cook 2 to 3 minutes on each side or until fish flakes easily when tested with a fork.
3. Spread about 1 tablespoon Greek Tapenade on each bread slice. Top each of 2 slices with 1 fillet, 2 tomato slices, 1/3 cup mâche, and remaining bread slices.