In a 10 inch fry pan combine the water, onion and garlic. Bring to a boil; reduce heat to simmer cover and cook for 5 minutes until onions are tender. Stir in the beans, tomato sauce, green chili peppers, chili powder and salt. Cover and simmer for about 10 minutes to heat all ingredients. In a separate bowl combine cornstarch with 1 tbs of water to smooth paste. Stir into the fry pan while stirring to thicken sauce.