- Cut tofu into ½-inch cubes; drain well on several layers of paper towels.
- Separate and rinse cabbage; pat dry.
- Cut leaves crosswise into 1-inch strips; set aside.
- Blend water, 1 tablespoon cornstarch and 3 tablespoons soy sauce; set aside.
- Cut tofu 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 tofu.
- Heat 1 tablespoon oil in hot wok or large skillet over high heat.
- Heat remaining 1 tablespoon oil in same pan.
- Add onion; stir-fry 2 minutes.
- Add cabbage; stir-fry 1 minute.
- Add tomatoes; tofu, and soy sauce mixture.
- Cook and stir gently until sauce boils and thickens.
- Gently fold in tofu; heat through.