Combine the tomatoes, onion, carrot, bell peppers, garlic, chiles (if using) and water in a medium saucepan and bring just to a boil over medium-high heat. Reduce the heat to medium and simmer until the vegetables are tender, 10 to 15 minutes. Let cool, then scoop the vegetables into a blender, add the water from the pan, and blend until smooth. Return the puree to the saucepan and stir in the oregano with salt to taste. Bring the salsa just to a boil, then set aside to cool. Transfer to a bowl; cover and store in the refrigerator if made ahead. Makes 2 1/2 cups; extra can be saved for other uses.