Chipotle Sauce: Toss the tomatoes in vegetable oil and preferably grill the onions, and the tom atoes, over Mesquite coals. The tomatoes should have blistered skins (if not gr illing, blister tomatoes skins in a very hot skillet and then add the onions wi th 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 ri nsed 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 lime juice and s alt and pepper to taste. For spicier sauce, add some of the adobo from the cann ed chilies.