Remove the stems and seeds from the dried chile pods. Toast the chile pods in a heavy skillet over medium heat until they are warm and release their fragrance, 1 to 2 minutes per side.
Remove the chile pieces and place into a sauce pan and cover with water. Bring to a boil, reduce the heat and simmer for about 10 minutes until the chile is soft.
Remove the chile from the liquid and place into a blender or food processor. Blend until a smooth paste. Strain the paste, pushing through with the back of a spoon. This takes a few minutes. You just want to keep straining, pushing the puree through leaving behind any skin or seeds, adding a lilttle water if you need to.
Warm the oil in a skillet, add the onion and garlic and cook until the onion is limp. Add the chile mixture to the onion mixture, along with the oregano and salt , adding more water. You want a pourable sauce, not a thick sauce. Cook for about 15 minutes, taste and adjust the seasonings. When ready the sauce will coat the back of a spoon but still be pourable. At this point I always strain again, pushing through the sauce, leaving behind any solids. This is not mandatory, but if I'm making enchiladas I want a very smooth sauce. Enjoy!