Pierce potatoes with a fork, and arrange in a circle on paper towels in microwave oven. Cover potatoes with damp paper towels. Microwave at HIGH 12 minutes or until done.
Heat a large nonstick skillet coated with cooking spray over medium-high heat.
Add onion, mushrooms, and oregano; coat with cooking spray. Cook 6 minutes or until tender.
Remove from heat; stir in parsley.
Preheat oven to 35
Cut potatoes in half lengthwise, and scoop out pulp, leaving a 1/4-inch-thick shell. Arrange shells on a baking sheet. Set aside.
Beat potato pulp, milk, and next 4 ingredients in a large bowl with a mixer at medium speed until smooth. Stuff shells evenly with potato mixture. Top with mushroom mixture.