Remove stems and seeds of the red chilies and put to soak in a large pot of water for several hours.
When the chilies are soft, blend them in a blender with the garlic cloves, oregano leaves, the chopped onion, sugar, and vinegar with enough water that the mixture is only slightly thickened (it should cling to the end of a spoon). It is best to start out with only a small amount of water (1/2 to 3/4 cup) adding more as the mixture blends to a smooth consistency.
In a large pot or a large casserole dish, pour the chile sauce over the pork cubes. Layer the sliced onion on top.
Cover loosely with plastic wrap and refrigerate for at minimum of 24 hours (48 hours will make it better, but 24 will work). If you don’t have 24 hours for marinating, then you can vacuum seal it and chill it for 24 hours and it is as good if not better.
Once the meat has marinated, place it in a slow cooker or heavy pot along with the marinade.
Slow Cooker - Using your slow cooker, cook on low for a minimum of 12 hours. This can be kept going by adding additional water as the meat mixture begins to look “dry”. The completed sauce should be rich and thick, not watery. You can let it simmer all day in your crock pot.
Stovetop - Using a large pot on the stove, cover and simmer gently until the meat is very tender, approximately 2 to 4 hours. The completed sauce should be rich and thick, not watery. It also can be brought to a boil on the stove then transferred to a 350 degree oven and baked, covered, for 2 hours.
Variation: For those of you out there who love to barbeque, this meat can also be cooked in that manner, but will not be able to keep as with the above method. To do this, place the meat in an aluminum pan (preferably disposable), and cover tightly with heavy aluminum foil. Place the meat close to the coals and allow to cook until done (160 degrees F.).
* These dried chile peppers can be found already dried in packaged in bags in the ethnic food section and/or produce section of most supermarkets.
Red Chile Pork Stew Recipe - Carne Adovada: https://whatscookingamerica.net/CynthiaPineda/CarneAdovada.htm