How to Make It
Preheat the broiler and set a rack 8 inches from the heat. Arrange the tomato halves on a rimmed baking sheet, cut sides down. Broil the tomatoes until the skins are charred and blistered, about 5 minutes. Turn the tomatoes cut sides up and broil until charred in spots, about 5 minutes longer. Discard the tomato skins.
Meanwhile, in a medium skillet, heat the corn oil. Add the chopped garlic and cook over moderately low heat until golden, about 3 minutes. Add the árbol chiles to the skillet and cook until softened slightly, about 2 minutes.
Scrape the chiles, garlic and oil into a food processor. Add the water and pulse, scraping down the sides as necessary, until a chunky puree forms, 2 minutes. Add the tomatoes, cumin and oregano and pulse until a chunky salsa forms. Season with salt and serve.