Cook breakfast pork sausage in a skillet with mushrooms and onions in 6-8 minutes or until sausage is done, stirring occasionally. Drain.
Meanwhile, heat cooking spray in another medium nonstick skillet on medium-high heat. Add potatoes; cook 8 to 10 min. or until browned, stirring occasionally. Spread potatoes to evenly cover bottom of skillet.
Combine sausage, onion, and mushroom mix and eggs; pour over potatoes. Cover. Simmer on medium-low heat 12 min. or until center is set.