Disney says
Swiss, Mozzarella, and Double Crème Brie fried in a light batter, dusted with Powdered Sugar, and served with a Berry Purée.
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Friendliest.app says
The gluten-friendly monte cristo sandwich is free of gluten/wheat, fish, shellfish, peanuts and tree nuts.

This meal contains milk, eggs and soy. It is served with an alternate side to the pomme frites, which are not gluten-friendly.

Note: To order a gluten-friendly monte cristo sandwich, you need to make accommodations 48 hours ahead of you visit by calling Dining Information (714-781-3463).