Heat the oven to 375°F. Lightly coat an 11 × 7-inch baking dish with cooking spray and place it aside.
Cut the chicken tenderloins into bite-size pieces measuring roughly 1 inch. Arrange the chicken evenly in the prepared baking dish, then toss it with the salt and black pepper until the pieces are evenly seasoned.
In a small bowl, whisk the condensed cream of celery soup, condensed cream of chicken soup, and milk together until the mixture is smooth and uniform.
Pour the soup mixture over the seasoned chicken. Spread it across the dish so the chicken pieces are evenly coated.
Scatter the chicken stuffing mix evenly over the creamy chicken layer. Slowly pour the chicken broth across the stuffing, making sure the dry mixture is thoroughly moistened for consistent texture during baking.
Cover the baking dish securely with aluminum foil and bake for approximately 40–45 minutes.
Remove the foil and return the casserole to the oven for another 5 minutes, allowing the surface to become lightly browned.
Confirm that the chicken has reached an internal temperature of 165°F before serving. Garnish with chopped parsley if desired. Spoon some of the flavorful gravy collected at the bottom of the baking dish over each portion when serving.