Bring a large pot of salted water to a boil. Add the string beans and cook for 2 minutes, plunge into cold water. Drain well and cut each bean in half. Halve the tomatoes lengthwise and remove the seeds. Slice the halves into 1/8-inch strips. Roughly chop all but 2 tablespoons of peanuts. In a bowl toss papaya with the beans, tomatoes, chopped peanuts, fish sauce, lemon and lime juices, sugar, garlic, red pepper flakes and 3 tablespoons cilantro. Garnish with remaining peanuts and cilantro.