Cut tofu into 1 cm cubes; drain well on several layers of paper towels. Separate and rinse cabbage; pat dry. Cut leaves crosswise into 3 cm strips; set aside. Blend water, 1 tablespoon cornstarch and 3 tablespoons soy sauce; set aside. Cut pork into thin slices, then into thin strips. Combine remaining 1 tablespoon cornstarch and 1 tablespoon soy sauce, ginger, garlic and sugar in small bowl; stir in pork. Heat 1 tablespoon oil in hot wok or large skillet over high heat. Add pork and stir-fry 2 minutes; remove. Heat remaining 1 tablespoon oil in same pan. Add onion; stir-fry 2 minutes. Add cabbage; stir-fry 1 minute. Add tomatoes; pork, and soy sauce mixture. Cook and stir gently until sauce boils and thickens. Gently fold in tofu; heat through.