1. Drain pineapple, reserving 1/4 cup syrup. Line sides of a 10 x 6-inch baking dish with pineapple, slightly overlapping; arrange yams in center. Pour pineapple syrup over yams.
2. Combine flour, brown sugar, cinnamon and salt. Cut in margarine until mixture resembles coarse crumbs; stir in nuts. Sprinkle over yams.
3. Bake at 350 degrees F. for 25 minutes. Top with marshmallows. Broil until lightly browned.