1. In a frying-pan, heat 1 tbsp oil and fry garlic until fragrant. Add vegetables and continue stir frying until wilted. Add salt and butter to season. Let it cool to room temperature.
2. Transfer the vegetable in a medium bowl and add all ingredient A. Knead mixture with hands thoroughly until the mixture forms sticky and moist.
3. Take a small portion of the mixture, and shape it into a flat, round disc shape, and then put a piece of mozzarella on it. Fold the meat mixture over it and make it into a round ball. Coat the balls lightly with katakuriko/potato starch. Repeat until all of the meat mixture is used.
4. In a skillet, heat 2 tbsp vegetable oil over medium-high heat and place the patties. Fry them on both sides until nicely brown. Reduce the heat to low and simmer for about 15 to 20 minutes with lid on.
5. Move the cooked patties to a plate. Add all the sauce ingredient to the skillet (don't wash it) and bring it to a boil over medium-high heat. Reduce the heat to low and place the patties back onto the sauce. Let them cook for a few minutes.