Pre-heat the oven to 400°F.
Lightly pound the chicken breasts and season both sides with salt and pepper.
In a bowl, combine the tomatoes, haricots verts, shallots, garlic, olive oil, tarragon, salt and pepper; toss to combine.
Cut four 12-inch x 16-inch pieces of parchment paper (you can buy pre-cut packaged half sheets from any restaurant supply store).
Arrange about a quarter of the bean mixture in the center of each parchment, top with a chicken breast and tablespoon of butter and some parsley.
Fold the papers’ short ends at the middle, folding them over an inch, then a few more turns; fold in the ends to make half-moon shaped packets (sacks). Roast the chicken for 25-30 minutes and remove from the oven.
Place on plates. Open the parcels carefully and slide the vegetables and chicken off the paper. Discard the paper.