Preheat the oven to 400 degrees and line a baking sheet with parchment paper.
In a large bowl, combine the ground turkey, breadcrumbs, egg, 1/4 cup ketchup, diced onion, garlic powder, salt, and pepper. Mix gently until everything is evenly distributed.
Divide the mixture into four equal portions and shape each into a small loaf. Place the loaves on the prepared baking sheet and spread 2 tablespoons of ketchup over the tops.
Bake the meatloaves for 20 to 25 minutes until they reach an internal temperature of 165 degrees.
While the meatloaves bake, place the cubed potatoes in a large pot and cover with cold water. Add the 1/2 teaspoon salt and bring to a boil. Cook until the potatoes are fork-tender, about 15 minutes.
Drain the potatoes and return them to the pot. Add the milk and butter, then mash until smooth and creamy. Serve the meatloaves alongside the mashed potatoes.