Mexican tomato sauce can be mild or spicy depending on whether or not you use chiles. The main ingredients in Mexican tomato sauce are tomato, onion, garlic, and salt. When making this recipe to be used in fideo seco or albondiga soup, adding a chile chipotle in adobo sauce or rehydrated chile guajillo adds spice and flavor. It is recommended to start with a small amount of chilies and adjust to your taste.