Preheat the oven to 400°F (200°C).
Wash and dry the russet potatoes. Pierce each potato several times with a fork.
Rub the potatoes with 1 tablespoon olive oil and sprinkle with 1/2 teaspoon salt. Place them on a baking sheet and bake for 45-50 minutes until tender when pierced with a fork.
Remove the potatoes from the oven and let them cool slightly until safe to handle.
Reduce the oven temperature to 350°F (175°C).
Cut each potato in half lengthwise and carefully scoop out the flesh into a large mixing bowl, leaving about 1/4 inch of potato flesh inside the skins to maintain their shape.
Add the sour cream, whole milk, melted butter, garlic powder, smoked paprika, remaining 1/2 teaspoon salt, and 1/4 teaspoon black pepper to the potato flesh. Mash until smooth and creamy.
Fold in the shredded chicken, 1/2 cup shredded cheddar cheese, chopped green onions, and crumbled bacon. Mix until well combined.
Place the potato skins in a greased 9×13-inch casserole dish, open side up.
Spoon the potato and chicken mixture evenly into each potato skin, mounding slightly.
Sprinkle the remaining 1/2 cup cheddar cheese and the mozzarella cheese evenly over the filled potato skins.
Drizzle the remaining 1 tablespoon olive oil over the top of the casserole.
Bake the casserole at 350°F (175°C) for 20 minutes, or until the cheese is melted and bubbly and the casserole is heated through.
Remove from the oven and let cool for 5 minutes before serving.