Preheat the oven to 400 F. Place the potatoes on a baking sheet and rub them with vegetable oil. Bake for 45 minutes or until they are tender. Let them cool slightly, peel, and cut in four.
While the potatoes are baking, cook the bacon in a skillet on low heat until crispy on both sides. Transfer to a plate lined with paper towels, let cool, and chop.
Place the cooked potatoes in a bowl. Pour in the milk and add the sour cream, sliced butter, one cup of shredded cheddar, seasoned salt, pepper, chives, and ⅔ of the chopped bacon. Mash with a potato masher until all ingredients are well incorporated.
Reduce the heat of the oven to 350 F. Place the mashed potatoes into a 7x11-inch casserole dish.
Sprinkle ½ cup of shredded cheddar and the remaining ⅓ chopped bacon on top. Bake for 20 minutes or until the cheese is melted and the mashed potatoes are heated through. Serve with sliced green onions on top.