Spray the inside of a 6 quart oval slow cooker with cooking spray.
Arrange chicken in a single layer on bottom. Season with poultry seasoning, lemon pepper, garlic and salt.
In a skillet on the stovetop, cook the onion and celery with butter over medium-high heat. Cook until softened and beginning to brown. about 3-5 minutes Season with black pepper to taste..
In a medium-size mixing bowl whisk together, both soups, chicken broth and gravy mix. Pour ¾ evenly over chicken in crockpot.
Add the stuffing/dressing mix and cooked vegetables to remaining soup in bowl. Mix well then spread on top. Cover opening with doubled paper towels, then place lid firmly into place.
Cook for 3-4 hours on high or 6-7 hours on low. Allow to sit uncovered for 15 minutes prior to serving. May fluff dressing with a fork, if desired.