Cook pasta according to directions while making sauce.
In large frying pan, put water, garlic and onion. Add part of vegetable broth if needed, to sauté onion for 3 minutes, stirring occasionally.
Add mushrooms and spinach and sauté 3 more minutes. Add remaining ingredients except cornstarch. Cook over medium heat, stirring occasionally about 12 minutes. Add cornstarch mixture and stir until thickened.