Preheat the oven. Preheat to 350°F. Lightly grease a baking dish large enough to hold the chicken breasts next to each other with room for the extra stuffing.

Cook the sausage and vegetables. Add 1 tbsp olive oil to a pan over medium heat. Add the onion and celery and cook for 5-6 minutes until soft. Squeeze the sausage out of the link casings into the skillet and discard the casings. . Cook over medium heat, breaking the sausage into small crumbles, until it is cooked through and the vegetables have softened. Add a little olive oil if the skillet seems dry.

Add the apple. Stir in the diced apple and cook for a few minutes, until it begins to soften.

Prepare the stuffing. While the veggies and sausage are cooking, prepare the stuffing according to the package directions, using the water and butter called for on the box. Follow the package’s order for adding the liquid and stuffing mix. Pour the cooked stuffing into the pan  with the sausage, onion, celery and apple and mix well. Remove from heat.

Butterfly the chicken. Place each chicken breast flat on a cutting board. Slice horizontally through the middle, stopping before cutting all the way through, then open it like a book. Do not pound or flatten it. Season with olive oil, salt, pepper, onion powder, and garlic powder.

Fill and arrange. Spoon the sausage stuffing mixture inside each chicken breast. Place the filled breasts next to each other in the prepared baking dish, with the stuffing peeking out. Spoon the remaining stuffing around the chicken.

Bake. Bake for 40–45 minutes, or until the thickest part of the chicken and the center of the stuffing reach 165°F. If the stuffing browns too quickly, loosely cover the dish with foil. Larger breasts may need additional time.