Place the chicken thighs, water, celery, onion, carrots, garlic, parsley, bay leaf, kosher salt, and pepper into the removable cooking pot.
Close and lock the lid and set the valve to the PRESSURE position. Pressure cook on HIGH pressure for 35 minutes. When the time is up, let the pressure release naturally for 30 minutes.
While the soup cooks, prepare the matzo ball mixture. In a large bowl, whisk the eggs until just slightly beaten.
Add the vegetable oil, matzo meal, salt, and baking powder. Place the mixture into the refrigerator until you are ready to make the matzo balls.
Remove the chicken thighs and vegetables with a slotted spoon to a large bowl and set aside.
Strain the broth through a fine-mesh strainer and discard the solids. Pour the broth back into the cooking pot bring to a boil using the SAUTÉ function.
Wet your hands and shape the matzo mixture into small balls, it should yield about 13 to 15 balls.
Place the matzo balls into the boiling broth. Place the lid on the cooker and switch to the SIMMER function for 40 minutes.
As the matzo balls simmer, chop the cooked vegetables into smaller pieces. Remove the chicken from the bones and discard the skin and bones. Chop the chicken.
Add the chopped vegetables and chicken back to the broth with the matzo balls and heat through.
Season with dill or parsley if desired.