Combine onions, tomatoes, vinegar, garlic, chipotle chiles, oregano, marjoram, salt, thyme, cumin, and brown sugar in a blender and blend until smooth.

Combine chicken broth, chicken, and blended sauce in the inner pot.

Close the lid and pressure cook on High Pressure for 12 minutes.

Do a Natural Pressure Release (NPR). If you're short on time, you can do a 15 minute Natural Pressure Release (NPR 15). [Read More: The Different Pressure Release Methods]

Using a slotted spoon, transfer the chicken from the inner pot into a large bowl and reserve.

Select Saute mode and reduce the sauce until thickened, about 7 to 10 minutes, stirring intermittently. To prevent splatter from the bubbling sauce, use a splatter screen to protect your countertops.

Shred the reserved chicken using a meat shredder or two forks. Add in desired quantity of sauce (about ¼ to ½ cup) and stir together the chicken and sauce.

Heat a large nonstick frying pan over medium-high heat and 2 teaspoons of vegetable oil. [See Note 1].

Spread out the shredded chicken on the frying pan without overcrowding. Add more sauce if desired.

Saute the chicken until brown bits form on the bottom, stirring gently occasionally. Add more sauce as needed.

Transfer chicken to a serving bowl. Serve with tortillas, rice or salad and your choice of toppings.

Combine onions, tomatoes, vinegar, garlic, chipotle chiles, oregano, marjoram, salt, thyme, cumin, and brown sugar in a blender and blend until smooth.

Heat a large saucepan over medium-high heat. Add chicken broth, chicken, and blended sauce to the saucepan and bring to a boil. Reduce heat to medium-low and simmer until the chicken is cooked through, stirring occasionally, about 30 minutes. Transfer chicken pieces to a large bowl and set aside.

Reduce the remaining sauce until thickened.

Once the chicken is cool enough to handle shred the reserved chicken using a meat shredder or two forks. Add in desired quantity of sauce (about ¼ to ½ cup) and stir together the chicken and sauce.

Heat a large nonstick frying pan over medium-high heat and 2 teaspoons of vegetable oil. [See Note 1].

Spread out the shredded chicken on the frying pan without overcrowding. Add more sauce if desired.

Saute the chicken until brown bits form on the bottom, stirring gently occasionally. Add more sauce as needed.

Transfer chicken to a serving bowl. Serve with tortillas, rice or salad and your choice of toppings.