In a medium bowl, combine the can of whole-berry cranberry sauce and the can of undiluted condensed cream of chicken soup. Stir them together until reasonably well blended — you do not need a perfectly smooth mixture, and the cranberries do not need to be fully broken down. A few streaks and lumps in the sauce at this stage are completely fine and will smooth out during the long cooking time. If you are adding any of the optional ingredients — Dijon mustard, orange juice, onion soup mix, or dressing — stir them into this mixture now.
Step 3: Layer and Cover
Place the raw chicken breasts in a single layer in the bottom of the prepared slow cooker. If the breasts are very large and thick, you can butterfly them or cut them in half to help ensure more even cooking throughout. Pour the cranberry sauce mixture evenly over the chicken, making sure each piece is well coated and the sauce covers the chicken generously. You do not need to add any additional water, chicken broth, or other liquid — the condensed soup provides adequate moisture, and the chicken will release its own juices during cooking, which will thin the sauce naturally to the right consistency.
