Slice half of the lotus root into thin discs. Put the remaining half into a ziploc bag and crush it finely (use a rolling pin or something similar to crush it).
Put the crushed lotus root, ground chicken, minced ginger, salt, and corn starch into a bowl and mix well.
Form little meatballs out of the mixture and flatten into patties. Press a lotus root disc into the top.
Heat a frying pan on medium and add sesame oil. Put the patties lotus root side down and cook. Turn over once browned, reduce the heat to medium-low, and cover with a lid. Cook the other side for 5 minutes.
Add the sake, mirin, sugar, and soy sauce into the pan, mix, and then boil it down for a couple of minutes until it thickens a little.
Flip the patties around a couple of times to make sure they're coated in the sauce and then serve (or save for your bento).