Prep the Base: Layer the diced onion on the bottom of your slow cooker. Place the chicken thighs in a single layer directly on top of the onions.
Mix the Gravy: In a mixing bowl, combine the cream of chicken soup, cream of celery soup, poultry seasoning, fresh chopped parsley, and black pepper. Stir until smooth.
Combine: Pour the soup mixture evenly over the chicken thighs. Pour the 2 cups of chicken broth over the top of the entire mixture.
Slow Cook: Cover with the lid and set the crockpot to HIGH. Cook for 4 hours.
Shred and Add Veggies: After 4 hours, remove the lid. Shred the tender chicken thighs directly in the pot using two forks. Pour in the 2 cups of defrosted mixed vegetables and stir well to combine.
Prep Dumplings: Open the can of refrigerated biscuits. Press each biscuit flat, then slice each one into 4 long strips.
Cook Dumplings: Layer the sliced biscuit dough over the top of the hot chicken and vegetable mixture. Replace the lid immediately.
Final Hour: Cook on HIGH for 1 final hour to steam the dumplings. Do not open the lid during this time! 9. Serve: Once the hour is up, gently stir the mixture together to incorporate the fluffy dumplings into the creamy chicken base. Garnish with additional freshly chopped parsley and serve hot.