Coat a 10-inch nonstick skillet with cooking spray; place over medium-high heat until hot. Add mushrooms and green onions; saute until tender. Remove from skillet. Set aside, and keep warm.
Add spinach to skillet, and saute until spinach wilts. Remove from heat; stir in cream cheese. Remove from skillet. Set aside, and keep warm.
Wipe skillet with a paper towel. Combine egg substitute and next 3 ingredients in a small bowl, stirring well.
Coat skillet with cooking spray; place over medium heat until hot. Pour egg substitute mixture into skillet. As mixture begins to cook, gently lift edges of omelet with a spatula, and tilt pan to allow uncooked portion to flow underneath. When set, spoon mushroom mixture, spinach mixture, and Cheddar cheese over half of omelet. Loosen omelet with a spatula, and carefully fold in half. Cook an additional 1 to 2 minutes or until cheese begins to melt. Slide omelet onto a serving plate, and cut in half. Sprinkle with parsley.