In a medium saucepan, cook onion and garlic in the oil until tender but not browned. Stir intomatoes, chili peppers, chili powder and hot pepper sauce. Boil uncovered for 10 minutes. Stir together cornstarch and 1 Tablespoon cold water; stir into tomato mixture and cook stirring constantly untill thickened and bubbly. Add cheese to mixture and stir till its melted. Serve warm with tortilla strips.