Preheat the oven to 350 degrees F.
Place the chicken presentation-side down on a baking tray and sprinkle with half of the salt, tarragon, pepper, thyme and garlic. Flip the chicken, then sprinkle with the remaining salt, pepper and garlic. Spoon the oil over the chicken and rub to fully coat. Add the remaining thyme and tarragon, and then bake until the internal temperature is 165 degrees F, about 40 minutes.
Meanwhile, place the bacon on a foil-lined baking sheet and bake in the same oven for 8 minutes, then rotate the baking sheet and bake 8 more minutes. The bacon should be almost fully cooked.
Chill the chicken until fully cooled.
Using a very sharp knife, slice the chicken on a vertical bias across the breast into 1/8-inch-thick slices.
Halve the ciabatta horizontally, then set it up open-face to build the sandwiches. Spread half of the ranch dressing onto the bottom piece of ciabatta. Stack the sliced chicken over the ranch, creating two or three layers. Cover the chicken with the sliced Cheddar and then top with the bacon.
Bake both halves of the sandwich until the cheese melts, the bacon is crisp and the bread is toasted.
Coat the top piece of ciabatta with the remaining ranch dressing. Top the bacon with the avocado, and then finish the sandwich with the top piece of bread. Cut into 4 pieces to serve.
This recipe was provided by a chef, restaurant or culinary professional. It has not been tested for home use.