Combine potatoes, half the green onions, half the Parmesan cheese and half the pepper in large bowl.
Stir in half the eggs and mix until well blended.
Coat 8-inch tart pan (with removable bottom) with butter-flavored nonstick cooking spray.
Spread potato mixture evenly on bottom and up sides of pan.
Place tart on baking sheet and bake in preheated 475ºF oven 12 minutes or until golden brown.
Remove from oven.
Reduce oven temperature to 375ºF.
Heat oil in large skillet over high heat. Add mushrooms and cook three minutes; remove from heat. Stir in feta cheese, milk, thyme and remaining green onions, Parmesan cheese, pepper and eggs. Pour mushroom mixture into potato crust.