Preheat your oven to 350 degrees F (175 degrees C).
Place the chicken breasts on a baking sheet and rub them with olive oil.
Season generously with salt and pepper.
Roast the chicken in the oven for 35 to 40 minutes or until the internal temperature reaches 165 degrees F (74 degrees C).
Allow them to cool before cutting into bite-sized pieces.
In a large bowl, combine the diced chicken, celery, grapes, red onion, and tarragon.
Stir in the mayonnaise.
Mix well to ensure everything is coated evenly.
Finally, add the toasted almonds for a delightful crunch.
Taste and adjust the seasoning with salt and pepper if needed.