Preheat the oven to 425 degrees F (220 degrees C). Pierce potato skins with a fork.

Microwave potatoes on high for 12 minutes. Transfer partially baked potatoes to the preheated oven and bake for 15 minutes.

Remove potatoes from the oven, leaving the oven on. Slice off potato tops, then scoop out most of the flesh, being careful to leave the skins intact. Mash the flesh in a medium bowl.

Melt butter in a small skillet over medium heat. Add onions and sauté 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 until heated through, about 15 minutes. Season with parsley, salt, and pepper.