Cut the chicken breast into bite-sized pieces and season lightly with a pinch of salt and pepper.
Heat the olive oil in a medium pot over medium heat and sauté the chicken until golden on all sides.
Add the diced onion, carrots, and celery to the pot, cooking for 5 minutes until the vegetables begin to soften.
Pour in the chicken bone broth, dried thyme, and remaining salt and pepper, then bring the mixture to a gentle simmer.
In a small mixing bowl, whisk the egg and water together before stirring in the cassava flour and chopped parsley to form a thick dough.
Using a small spoon, drop rounded tablespoons of the dough into the simmering broth, making sure they are spaced apart.
Cover the pot with a tight-fitting lid and let the dumplings steam for 10 to 12 minutes without lifting the lid.
Once the dumplings are firm and the chicken is fully cooked, ladle the soup and dumplings into a bowl and serve immediately.