Preheat the oven to 375°F and line a baking sheet with parchment paper.
In a large bowl, combine the ground chicken, 1/4 cup teriyaki sauce, breadcrumbs, egg, green onions, garlic, and ginger. Mix until evenly blended, then divide the mixture into four equal portions and shape each into a small loaf. Place the loaves on the prepared baking sheet and brush the tops with the remaining 1/4 cup teriyaki sauce.
Bake the meatloaves for 25 minutes. While they bake, place the potatoes in a saucepan, cover with water, and bring to a boil. Cook until tender, about 15 minutes, then drain.
Mash the potatoes with the milk, butter, salt, and pepper until smooth. Remove the meatloaves from the oven and spread the mashed potatoes evenly over each one. Return to the oven for 10 more minutes. Sprinkle with sesame seeds before serving.