Put Tofu, ground beef, Panko, salt and pepper in a large bowl and mix very well. Divide into 4 pieces and shape into oval patties.
Heat a frying pan at medium high heat with oil. Place patties in the pan and cook for 4-5 minutes. Turn them, lower heat, and cook another 4-5 minutes covered.
While cooking the meat, make the sauce. In a small bowl, mix Soy Sauce, Mirin, Sake, water, and cornstarch.
Add prepared sauce in the pan and cook until the sauce thickens. Serve with green onions.