Spray slow cooker with non-stick cooking spray. Place chicken breasts in the bottom of the slow cooker. Top with onion, potatoes, carrots, celery and frozen green beans.
In a mixing bowl, mix together cream soups, milk, dry ranch dressing mix, salt and pepper. Pour mixture on top of chicken and vegetables.
Place the lid on top of slow cooker and cook on low heat for 6-8 hours (start checking at 6 - you just want to make sure that your chicken is fully cooked and your potatoes and carrots are soft).
Stir everything together, then serve and enjoy!
Notes
If you do not love mushrooms and try to avoid them at all costs, you are welcome to use two cans of cream of chicken instead of one cream of chicken and one cream of mushroom.