Dice the chicken breast into bite-sized pieces and finely chop the carrots, celery, and onion.
Heat the olive oil in a medium pot over medium heat. Add the chicken and cook until lightly browned on all sides.
Add the carrots, celery, onion, and minced garlic to the pot. Sauté for 3-4 minutes until the vegetables begin to soften.
Stir in the chicken broth, dried thyme, dried rosemary, sea salt, and black pepper. Bring the mixture to a gentle simmer.
While the stew simmers, prepare the dumplings by mixing the oat flour, baking powder, and 2 tablespoons of Greek yogurt in a small bowl. If the dough is too dry, add a teaspoon of water until a thick, sticky dough forms.
Using a small spoon, drop marble-sized portions of the dumpling dough into the simmering broth. Cover the pot with a lid and simmer for 8-10 minutes.
Remove the pot from the heat. Carefully stir in the remaining 0.25 cup of Greek yogurt to create a creamy sauce without boiling the yogurt.
Serve immediately in a warm bowl, ensuring each portion gets plenty of herbs and dumplings.