Line sides of baking dish with pineapple and put yams in the center.
Combine flour, brown sugar, cinnamon and salt; cut in butter until mixture resembles coarse crumbs. Stir in nuts.
Pour reserved pineapple liquid over yams. Sprinkle with flour mixture. Bake at 350°F for 25 minutes. Top with marshmallows and then broil until lightly brown.