Make the chicken salad: Arrange a rack in the middle of the oven and heat to 425°F. Place the chicken on a rimmed baking sheet. Rub some olive oil over the chicken and season all over with salt and pepper. Roast until the chicken is cooked through, 25 to 30 minutes. The skin does not need to brown; you just want the meat to cook through.
Set the chicken aside on the baking sheet until cool enough to handle. Shred the meat and discard the skin and bones. (You should have about 3 1/2 to 4 cups of shredded chicken.) Place in a large bowl, and drizzle the chicken with a bit of the juices from the pan just to keep it moist. Add the celery, red pepper, almonds, onion, and parsley.
Make the sandwiches: Place 6 slices of bread on a work surface. Divide the chicken salad over the bread and spread into an even layer. Top each sandwich with French sauce, then close the sandwiches with the remaining bread slices.