1. Preheat oven to 350 degrees Fahrenheit (180 degrees Celsius). Coat a large Pyrex baking dish or nine- by 13-inch pan with nonstick cooking spray.
2. In a bowl, combine the ingredients for the honey mustard; set aside.
3. Place sliced onions and half the sliced apples into the pan. Top with chicken pieces. Sprinkle chicken liberally with salt and pepper.
4. Use a spoon to coat all the chicken pieces with the honey mustard. Sprinkle the breadcrumbs over the honey mustard till the chicken is fully coated.
5. Place remaining apple slices in the little nooks and crannies all around the chicken.
6. Spray the breadcrumbs with nonstick cooking spray.
7. Cover the baking dish tightly with foil. Bake for one hour and 20 minutes. Remove foil; continue baking until the top is crispy and the chicken is cooked to your taste. Serve hot and enjoy!