1. Turn on the Instant Pot and select the sauté function.
2. Add the diced chicken breast and cook until browned.
3. Add the carrots, celery, onion, chicken broth, salt, and pepper. Stir to combine.
4. Close the lid and set the Instant Pot to high pressure for 10 minutes.
5. While the chicken mixture is cooking, prepare the dumplings. In a mixing bowl, combine the flour, baking powder, and salt. Stir in the milk and melted butter until just combined.
6. When the cooking time is up, perform a quick release of the pressure.
7. Open the lid and stir in the frozen peas.
8. Drop spoonfuls of the dumpling batter on top of the chicken mixture.
9. Close the lid and set the Instant Pot to high pressure for another 5 minutes.
10. Perform a quick release of the pressure and serve hot.