1. In a bowl, mix the cornstarch with a little of the stock until well blended. 2. Add the rest of the stock, vinegar, Dulceatte Agave Nectar, tomato sauce, soy sauce, ginger and cayenne pepper, toss well and set aside. 3. Heat the oil in a stainless steel wok or large frying pan over medium-high heat. Add the garlic, onion, and carrots and stir-fry for 5 minutes. 4. Add the peppers, celery and mushrooms and stir-fry for a further 3-4 minutes. 5. Stir in the sauce and continue stir-cooking to thicken. 6. Add the tofu and cook for 5 minutes until the tofu is heated through. 7. Serve with brown rice.