Preheat the oven to 425 degrees. Grease a 9 x 13 inch casserole dish with non-stick cooking spray.
Prepare the stuffing. Bring the chicken broth and butter to a boil, then add the stuffing mix. Mix well, then cover. Rest for 5 minutes, then fluff the stuffing mixture with a fork.
While the stuffing mixture is resting, whisk together the salt, thyme, parsley, garlic powder, onion powder, and pepper in a small bowl.
Butterfly the chicken breasts by slicing them through the center horizontally, leaving about a ½ inch intact. Unfold the chicken like a book.
Brush the insides of the chicken with olive oil and sprinkle with some of the seasoning mix.
Add the stuffing mixture to the bottom side of the chicken breasts, dividing it evenly among the four pieces. Fold the top side over.
Place the chicken bottom side up in the casserole dish and brush generously with olive oil. Sprinkle with seasonings, then flip the chicken over. Brush the top side with oil and sprinkle with remaining seasonings.
Transfer to the oven and bake for 25-30 minutes, or until the thickest part of the chicken reaches an internal temperature of 160 degrees.