When preparing mushroom fillings for dumplings, the size of your dice is critical. Large or irregular chunks of mushroom can act like sharp points that puncture thin dumpling wrappers during cooking, causing them to burst open and leak their filling. Aim for a fine, even dice no larger than 3-4mm. This ensures the filling compresses smoothly when you seal the dumpling, without creating pressure points against the delicate dough. A fine dice also helps the mushrooms cook more evenly and integrate better with other filling ingredients like kimchi, creating a cohesive mixture rather than a collection of separate components inside your dumpling.