In a small bowl whisk together the 2tbsp water and 1 tbsp corn starch. Set aside. In a larger bowl whisk together the remaining sauce ingredients.
In a large ban or wok bring the sauce to a boil on high heat, reduce to medium, add the carrots, cover and simmer for 5 minutes.
Add the broccoli to the pan, bring back to a boil, reduce to medium, cover and simmer 5 minutes.
Stir in the mushrooms, tofu and onions. Cover and simmer another 5 minutes.
Uncover the pan, stir in the corn starch and water mixture, then add the green onions and simmer, stirring, for another 3 minutes. Serve over rice.