Saute' the onion and garlic with the cayenne pepper until soft. Add the ginger, peas, and broccoli. Cook over medium heat for about 5-7 minutes. Add the mushrooms and the tofu.
In a small bowl, mix together the soy sauce, 3 tbsp. water, and the corn starch. Slowly add to the cooked veggies, mixing constantly. The sauce should thicken and coat the veggies. If not thick enough, try heating a little longer, or adding a little more cornstarch and water mixture, until the sauce thickens.
Serve over prepared yellow rice.