Using your hands, mix the ground chicken, breadcrumbs, garlic powder, parmesan cheese, and salt & pepper together and form 1" meatballs.

Heat olive oil in a skillet or frying pan on medium-high heat. Add meatballs, taking care not to crowd the pan. Turn the meatballs every minute or two until they're browned all over.

Once meatballs are browned, remove them to a plate and set aside. Add onions to the pan and cook for about five minutes, stirring a few times.

Add mushrooms and garlic to the pan. Cook for another five minutes or so, stirring a few times.

Add the Dijon mustard and sour cream to the pan. At this point you can either add the meatballs back in if your skillet is deep enough (mine is about 2" deep), or add the pan contents and meatballs to a larger pot to cook from there. Turn the heat down to medium-low, cover, and cook for an additional 10 minutes (stir halfway through) or until the meatballs are cooked through. Add extra salt & pepper if desired.

Serve immediately. Great with mashed potatoes or egg noodles.