Chipotle Sauce: Toss the tomatoes in vegetable oil and preferably grill the onions, sliced 1 cm thick and the tomatoes, over Mesquite coals. The tomatoes should have charred skins (if not grilling, char tomatoes skins in a very hot skillet and then add the onions with some vegetable oil to a hot sauce pan) Add garlic and continue to cook for about 2 minutes. Add the oregano, cilantro, and the chilies, which have been rinsed and cleaned of their veins, and seeds and cook slowly, covered , for about 20 minutes . Let cool and then puree in the blender, adding the lim e juice and salt and pepper to taste. For spicier sauce, add some of the adobo from the canned chilies.