Heat oven to 350°F.
Cut each meat slice into 15 pieces. Cut apple into 30 slices, then cut each slice crosswise in half.
Place crackers in single layer on baking sheet; top with apples, meat and cheese.
Bake 3 min. or until heated through. Sprinkle with onions.
The meat, cheese and onions can be cut ahead of time. Refrigerate in separate airtight containers up to 12 hours before using as directed.