How to Make It
Preheat the oven to 325°. In a large skillet, cook the bacon over moderate heat until browned and crisp all over, about 5 minutes. Transfer the bacon to paper towels to drain, then cut each slice into 4 pieces.
Using a paring knife, cut a 1-inch round plug out of the top of each brioche roll. Carefully hollow out the rolls. Set the rolls on a baking sheet and warm them in the oven to refresh them, about 5 minutes.
In a medium bowl, combine the the mayonnaise, celery, shallot, minced parsley and lemon juice. Stir in the diced chicken and season the salad with salt and pepper.
Spoon 1 tablespoon of the chicken salad into each brioche roll, garnish with parsley leaves and cover with a tomato slice. Top each roll with 1 teaspoon of chicken salad, garnish with the bacon and serve.