First you want to prepare your tuna. After it has been cubed put it in a non reactive bowl. Add all of the juice from your citrus and salt and pepper. Stir and cover. Place back in the refrigerator for at least 2 hours. The acid from your citrus will cook the tuna. Blanch your italian beans for approx 5 minutes in boiling water and then rinse in cold water. Drain and rinse your canned beans. Dice your celery, peppers, and onion. Mix everything together and toss in your slice tomatoes. When the tuna is done drain it and then add it to your vegtables. Toss with your favorite dressing and refrigerate till ready to serve. This tastes even better the next day