Cut acorn squash in pieces in about 4 cm size. With spoon, scrape out seed and stringy portion. Peel the green skin off and cut. Cut half of ginger in thin strips, soak in water to crisp. Chop remaining ginger, about 1 teaspoon. In pan, place chopped ginger and Mixture A. Heat; add ground beef, stir constantly with chopsticks until liquid has cooked away. Place squash in pan (on top of beef); add Mixture B and water (just enough to almost cover squash). Place a smaller lid on top of squash. Before covering pan with its own cover, bring to boil. Reduce heat, simmer until tender. Remove squash, bring remaining mixture to a boil; stir in 2 teaspoons cornstarch mixed with water and cook until thickened. To serve: Place squash on plate, spoon on ground meat. Garnish with thinly cut ginger.