Pulse chickpeas, mayonnaise, lemon juice, and tarragon in food processor until chunky.Spread chickpea mixture on 4 bread slices. Top with beet and apple slices, and sprouts. Spread remaining 4 bread slices with tapenade; close sandwiches.Spray panini with cooking spray. Coat skillet or grill pan with cooking spray; heat over medium heat. Place panini in pan; weight with smaller-diameter saucepan weighted with 2 cans. Cook 3 minutes. Flip, replace weight, and cook 2 minutes. (Or cook 4 minutes in panini maker.)