Preheat an air fryer to 350 degrees F (175 degrees C).
Brush potatoes gently with 1 teaspoon oil; place into the air fryer basket and cook for 10 minutes. Brush potatoes with 1 more teaspoon oil; continue cooking for 10 minutes. Coat with the remaining 1 teaspoon oil and cook until tender, about 10 more minutes.
Cut cooked potatoes in half. Spoon the insides into a bowl; add 1/4 cup Cheddar and mix well.
Cook onion and bacon in a skillet over medium-high heat, turning occasionally, until bacon is evenly browned, about 10 minutes.
Mix onion and bacon into mashed potatoes. Stuff mixture into potato skins. Sprinkle remaining Cheddar on top.
Return stuffed potatoes to the air fryer and cook until cheese is melted, about 6 minutes.