Preheat oven to 425 degrees F (220 degrees C). Pierce the skin of the potatoes with a fork.
Microwave pierced potatoes on HIGH for 12 minutes. Place partially baked potatoes in the preheated oven and bake for 15 minutes. Slice off potato tops, scoop out the bulk of the interior of the potato being careful to leave the potato skins intact. In a medium bowl, mash the removed potato interior.
Heat a small skillet over medium heat, stir in butter. Saute onions in the skillet until tender, about 5 minutes.
Combine onions, broccoli, and ranch dressing with the mashed potato. Brush the outside of the potato skins with oil. Spoon potato mixture into the skins. Arrange stuffed potatoes on a cookie sheet.
Bake potatoes for 15 minutes in the preheated 425 degrees F (220 degrees C) oven, or until heated through. Season with salt, pepper, and parsley.