HEAT oven to 400°F.
ADD hot water to stuffing mix; stir just until moistened. Remove stems from mushrooms; set caps aside. Chop stems. Melt margarine in large skillet on medium heat. Add stems and garlic; cook and stir 5 min. or until tender. Add stuffing, spinach and cheeses; mix well.
SPOON into mushroom caps. Place in shallow pan.
BAKE 20 min. or until mushrooms are tender and filling is heated through.
serving size = 1 stuffed mushroom (36 g)