Remove the skin from the chicken and if necessary, cut it into smaller pieces at the joints. Use a paper towel to wipe away any bone splinters at the cutting points. Season the chicken with 1 teaspoon salt. Put aside.
Heat the oil in a large saucepan over medium/high heat, add the onion, and stir and fry until it softens and turns a light golden brown.
Add the garlic, cook while stirring for about 1 minute.
Reduce the heat to low and add the cumin powder and chili powder, cook and stir for about 1 minute.
Add the diced tomatoes, chipotle in adobo sauce, and oregano mix well.
Add the chicken and use a wooden spoon to push it into the sauce.
Turn the heat to high and bring to a boil, reduce the heat to medium/low, cover the pot with a lid and simmer for about 40 – 50 minutes or until the chicken is cooked. Stir the sauce from time to time to prevent it from sticking to the bottom of the pot and burning.
Remove the chicken from the pot and transfer to a plate, allow to cool to a temperature that is comfortable to handle. When the chicken is cool enough to handle, remove and discard the bones. Use your hands or two forks to shred the meat. Put aside.
Continue to cook the sauce uncovered, over medium/high heat until it thickens to a salsa-like consistency. This will take about 10 – 15 minutes. You will need to constantly stir the sauce, and as the sauce thickens reduce the heat slightly. It should be thick and almost paste-like.
Return the shredded chicken to the pot with tomatoes and stir over medium heat until the chicken is fully coated in the sauce and reheated. Taste for salt and pepper and adjust to taste.