- Start by making mashed potatoes: Peel and cube potatoes, then bring to a boil in a large pot of water. Cook until tender, about 10 minutes. Strain potatoes and add to a mixing bowl. Use a potato masher or hand mixer to mash potatoes until chunky. Add sour cream, whole milk, butter, salt, garlic powder, pepper and half of the chives. Continue to mix until ingredients are combined and potatoes are fluffy. Set potatoes aside.
- Lightly grease a 9-inch pie pan. Heat olive oil over medium heat in a medium skillet and add carrots and onions. Sauté for 6 minutes, stirring regularly. Move vegetables to side of pan and add ground chicken. Break up into small crumbles. Stir in mushrooms and jalapeños, cook 6 minutes longer, stirring regularly. Drain and discard liquid from pan.
- Stir in teriyaki takumi sauce to evenly coat chicken and vegetables. Pour chicken mixture into prepared pan and smooth evenly.
- Top with large dollops of mashed potatoes. Smooth potatoes with a fork. Transfer to oven and broil on high for 6-8 minutes, until top is golden brown.
- Serve hot, topped with remaining chives and sesame seeds.