PREHEAT oven to 350°F. Reserve 1 Tbsp. onions for garnish; set aside. Combine cream cheese and remaining onions until well blended.
HEAT oil in large skillet on medium-high heat. Add plantains; cook 7 to 10 min. or until golden, turning frequently. Layer half of the plantains in 9-inch pie plate or baking dish sprayed with cooking spray. Spread cream cheese mixture over plantains; sprinkle with 1 cup of the shredded cheese. Top with remaining plantains and shredded cheese.
BAKE 20 min. or until cheese is bubbly and melted. Sprinkle with reserved 1 Tbsp. onions.