Spread the diced onion evenly across the bottom of a 6-quart slow cooker.

Arrange the boneless, skinless chicken breasts over the onions.

In a medium bowl, combine the cream of celery soup, cream of chicken soup, chopped parsley, poultry seasoning, and black pepper.

Spoon the creamy soup mixture evenly over the chicken.

Pour the chicken broth around and over the ingredients. Cover the slow cooker.

Cook on HIGH for approximately 4 hours before adding the vegetables and dumplings. The complete cooking process will take about 5–5 1/2 hours.

About 60–90 minutes before serving, gently roll or press each refrigerated biscuit into a thinner, flatter shape.

Cut each flattened biscuit into four strips or bite-sized dumpling pieces.

Add the thawed vegetables to the slow cooker and gently stir them into the creamy broth.

If the chicken is fully cooked and tender at this stage, shred or break it into bite-sized pieces directly in the slow cooker using two forks.

Arrange the biscuit strips over the surface of the Crock Pot Chicken and Dumplings, leaving a little room between pieces when possible.

Immediately replace the lid to prevent too much heat from escaping.

Continue cooking on HIGH for another 60–90 minutes, or until the biscuit dumplings are cooked through and no longer raw or doughy in the center.

Check that the chicken has reached at least 165°F (74°C) before serving.

Gently stir, if desired, to coat some of the dumplings with the creamy broth. Serve warm with additional parsley and black pepper.