If possible, grill the tomatoes over a charcoal or wood fire until they are soft but the skins have not blackened. Otherwise, broil them for 5 to 8 minutes, turning them frequently, until they are soft and the skins are blistered. Puree in a blender and set them aside.
Preheat the oven to 350°F.
Roast the garlic cloves until they are soft inside and slightly browned on the outside, about 20 minutes. Let them cool briefly; then peel. Put them in a small blender jar, and blend with some of the tomato puree.
Roast the chilies in the oven until they puff up and are fragrant about 3 to 5 minutes. Remove the stems, seeds, and veins, tear into pieces, then blend in a small blender jar or spice mill.
Roast the oregano in a dry skillet until it is aromatic, and remove it to a dish to stop the cooking.
Heat the tomatoes; season them with the garlic puree, chili, oregano. and salt, and simmer for 15 to 20 minutes.
Makes about 3 cups (6 one-half cup servings)