Heat dressing in medium skillet on medium-high heat. Add mushrooms, spinach, onions and garlic; cook 18 min. or until mushrooms are tender and liquid is cooked off, stirring occasionally. Stir in corn and Singles pieces; cook and stir 2 to 3 min. or until Singles are melted. Remove from heat; cool completely.
Roll out dough disks, 1 at a time, on lightly floured surface to 5-1/2-inch diameter. Spoon mushroom mixture onto centers of dough rounds, adding about 1/3 cup to each. Lightly moisten edges with water; fold in half to enclose filling. Press lightly on tops to remove air pockets; seal edges with fork.
Heat oil in medium deep skillet to 375ºF. Add 3 or 4 empanadas; cook 3 to 4 min. or until golden brown on both sides, turning after 2 min. Drain on paper towels. Repeat with remaining empanadas. Cool slightly.