HEAT oven to 400ºF.
PRESS pastry onto bottom and up side of 9-inch pie plate sprayed with cooking spray; trim edge.
HEAT oil in large skillet on medium-high heat. Add mushrooms; cook 5 to 7 min. or until mushrooms are tender and liquid is cooked off, stirring occasionally. Remove from heat; stir in ham. Spoon into crust; top with cheese.
WHISK remaining ingredients until blended; pour over ingredients in crust.
BAKE 30 min. or until knife inserted in center comes out clean. Let stand 10 min. before cutting to serve.