To prepare beans: Remove beans from their pods by first removing the string that runs along the pod. Then run your finger along the inside of the pod popping out the beans. Next, blanch the shelled beans in boiling water for 1 minute. Drain and plunge beans into ice water until completely cooled; then drain. Remove the waxy outer skins from beans by tearing the little flap at the top of the bean; then pinch the outer skin between your thumb and forefinger to pop out the bean.
Place onion and fennel in a mixing bowl and add zest, juice and oil. Mix together and let sit for about 3 minutes to marinate. Toss in beans, cheese, mint and black pepper; carefully mix to keep cheese intact. Transfer to small plates and serve.