Fill a medium saucepan with salted water and bring to a boil. Then add the cubed potatoes and cook until easily pierced with a fork, approx 10 minutes. Drain and return to the pot. Then add the garlic powder and the milk and mash using a potato masher until smooth.
Meanwhile, in a large skillet, add the oil and sauté your onion and carrots until softened, about 5 minutes. Then add the ground chicken and all the seasonings and cook until no longer pink, roughly 8 minutes.
Preheat your oven to 375 degrees F and line a 9"x13" baking dish with parchment paper.
Add the veggie and chicken mixture to the bottom of your baking dish in a single layer. Then add the mashed potatoes over top in a smooth, even layer. (I use a silicone spatula to help the potatoes spread across the top.)
Cover the tray with parchment paper and aluminum foil and bake in your preheated oven for 35 minutes. Then set your oven to broil, remove the paper, and broil for 5 minutes to get the potatoes nicely golden and crispy.
Remove from the oven and let stand for at least 5 minutes before slicing and serving. Enjoy!