Cut very thin slice from bottom of each tomato so it will stand upright. Cut thin slice from top of each tomato; scoop out tomato flesh, leaving tomato shell. Remove seeds from tomato flesh; chop enough tomato flesh to measure 1 cup.
In medium bowl, toss chopped tomato, tuna, beans, chopped parsley, capers, lemon juice, garlic, salt and pepper.
Spoon tuna mixture into hollowed-out tomatoes. Garnish with parsley sprigs.