Mince the onion and microwave it in a heatproof container covered with plastic wrap for 1 minute at 600W. Let it cool. Rub salt on the okra, rinse off, and slice into 5mm pieces.

In a bowl, mix ground meat, onion, salt, and pepper. Add the beaten egg and breadcrumbs, mixing thoroughly. Fold in the okra, divide into two portions, and shape into oval patties with an indentation in the center.

Heat vegetable oil in a frying pan over medium heat. Add the patties and cook until browned. Flip, cover with a lid, and cook on low heat for 8 minutes. Remove from the pan.

In the same pan, add the sauce ingredients (sake, mirin, sugar, soy sauce, water) and bring to a boil. Stir in the cornstarch slurry and cook until the sauce thickens.