In a large pot, melt the butter over medium heat. Add diced onion, sliced carrots, and celery. Cook until softened, about 5–6 minutes.
Add shredded chicken and chicken broth. Simmer for 5–7 minutes.
Stir in milk, garlic powder, salt, and pepper. Simmer an additional 2–3 minutes.
In a mixing bowl, combine Bisquick and milk. Stir gently until just combined.
Drop spoonfuls of dough onto the surface of the simmering stew. Do not stir.
Cover the pot and let the dumplings steam for 15–18 minutes, until cooked through and fluffy.
Check seasoning, garnish with parsley if desired, and serve hot.