Roast plum tomatoes and garlic on medium heat on cast iron skillet, in oven or in toaster oven until skin is charred and split and tomato is soft, about 30-40 minutes, turning occasionally to roast all sides. Remove stems from dried chiles and shake out seeds. Toast on each side for about a minute, high heat. Remove skin from tomatoes, if desired. Add all ingredients to blender or food processor and puree until smooth. Add salt and oregano to taste.