Toast fennel seeds in small skillet over medium-high heat until fragrant, shaking skillet occasionally, about 1 minute. Transfer seeds to medium bowl. Add olives, 2 tablespoons oil, garlic chives, orange juice, thyme, and orange peel to bowl and toss to blend. Season to taste with salt and pepper. DO AHEAD: Can be made 2 days ahead. Cover; chill. Bring to room temperature before using.
Prepare barbecue (medium-high heat). Brush both sides of bread slices with oil. Grill on 1 side until golden, about 1 minute. Turn bread over; immediately top each slice with 1 cheese round. Grill until bottoms are golden and cheese softens slightly, about 1 minute.
Transfer crostini to platter. Spoon olive mixture over and sprinkle with pepper.
Garlic chives, also known as Chinese chives, can be found at Asian markets.
