HEAT oil in large skillet over medium heat. Add onion and mushrooms and cook until tender and almost all liquid is evaporated. Remove from heat. Spray 12 inch pizza pan with cooking spray.
MIX egg, milk, pasta and 1/2 cup cheese. Spread pasta mixture in an even layer on prepared pan.
BAKE at 350°F. for 20 min.
SPREAD pasta sauce over pasta crust. Top with onion mixture. Sprinkle with remaining cheese. Bake for 18 min. or until cheese is melted and sauce is hot. Let stand 5 min.