- Combine soy sauce, sugar and 1/2 cup water.
- Brown beef in Dutch oven or large skillet over medium heat, stirring to break beef in large chunks.
- Add yellow onion; cook 1 minute. Add spinach, white parts of green onions, mushrooms and soy sauce mixture; cook until spinach wilts, stirring constantly.
- Gently stir in tofu and green onion tops. Cook about 5 to 7 minutes, or until vegetables are tender and tofu is seasoned with sauce.