In a large skillet melt the butter. Add the chicken and brown for 2 minutes on each side. Remove from the skillet and tent loosely with foil.
Add the mushrooms and saute until they are soft, about 4 to 6 minutes.
Whisk in the flour and then very slowly whisk in the chicken stock. Add just a few tablespoons at a time, whisking to combine it, until it is completely added.
Whisk in the milk, garlic powder, onion powder, salt and pepper.
Add the chicken back to the skillet.
Bring to a simmer, and cook, stirring often, over low heat for 13 to 15 minutes or until the chicken reaches 165 degrees with an instant read thermometer.
Serve over noodles.