Microwave pierced potatoes on High for 12 minutes or bake for 15 minutes.  Slice off potatoes tops. Scoop out pulp, keeping skins intact. Mash pulp in medium bowl. Heat a small skillet over medium heat, add butter. Add onion and sauté until tender, about 5 minutes. Add onion, broccoli, and salad dressing to potato pulp, mix well. Brush outside of potatoes skin shells with oil. Spoon potato mixture into shells, dividing evenly. Place on baking sheet. Top each potatoes with Cheddar cheese. Bake potatoes until heated through, about 15 minutes in a 425 degree oven. Sprinkle with parsley, salt and pepper to taste. Makes 4 servings.