Place the chicken breast in a casserole pan and cover with 1/2 cup of lemon juice and 1/2 cup olive oil. Refrigerate for 1 hour being sure to turn over after 1/2 an hour. Set a grill pan over medium heat and brush the grates with an oil soaked rag. Season the chicken with the Essence, 1 1/2 teaspoons of the salt, and 1 teaspoon of the white pepper. Place on the grill and cook, undisturbed for 4 minutes. Turn 90 degrees and cook another 4 minutes. Turn the chicken over and cook for 3 1/2 minutes. Turn 90 degrees again and cook for a final 3 1/2 minutes.
Remove the chicken from the grill and allow to cool completely. Once cool enough to handle, chop the chicken into 1/2-inch pieces and set into a medium-sized bowl. In the carafe of a bar blender, combine the egg, garlic, 1 tablespoon lemon juice and mustard. Pulse until well incorporated. With the blender running, slowly drizzle the 1 cup of oil through the feed tube into the carafe to form a mayonnaise. Season with 1/2 teaspoon of the salt and 1/2 teaspoon of pepper.
Pour the mayonnaise over the chicken and add the celery, red onions, celery leaves, parsley, tarragon, celery seeds, the remaining salt and pepper, ginger and cayenne. Toss to combine and cover with plastic wrap. Place in the refrigerator and store for at least 2 hours, and up to 1 day.
When ready to serve, toast the bread and place 2/3 cup of the chicken salad on top of each of the 6 sandwich bottoms and cover with the tops. Slice the sandwiches in half diagonally and serve with a light salad.