Cook:7 hrs to 8 hrs (low) or 3-1/2 to 4 hours (high) + 20 minutes (high)
In a 3-1/2- or 4-quart slow cooker whisk together the water and soup until combined. Add tomatoes, celery, carrots, onion, Italian seasoning, garlic, salt, and pepper; stir to combine.
Cover and cook on low-heat setting for 7 to 8 hours or on high-heat setting for 3-1/2 to 4 hours. If using low-heat setting, turn to high-heat setting. Stir in noodles; cover and cook for 20 to 30 minutes more or until tender, stirring once halfway through cooking. Gently stir in tofu cubes. Sprinkle with cheese; cover and let stand until cheese is melted.
To serve, sprinkle with chives and, if desired, chopped tomato.