HEAT oven to 400ºF.
USE rolling pin to flatten each bread slice to 5-inch square. Cut out centres with 3-1/2-inch round cookie cutter. Discard trimmings or reserve for another use. Press 1 bread circle onto bottom and up side of each of 12 muffin cups sprayed with cooking spray. Bake 8 to 10 min. or until golden brown.
REDUCE oven temperature to 350ºF. Meanwhile, whisk 1 egg and cream cheese spread in medium bowl until blended. Add remaining eggs, milk, ham and onions; mix well. Pour into bread shells.
BAKE 18 to 20 min. or until filling in centre of each cup is set. Serve warm.