In a 6-quart Instant Pot, add the chicken, orange juice, lime juice, soy sauce, oregano, cumin, cilantro, garlic, salt and pepper.
Lock the lid in place and set the vent to “sealing”. Select “manual pressure” (set to high) and set the timer for 10 minutes.
Once the timer goes off, let it naturally release for 10 minutes, then manually release any more pressure, then press “cancel”. Press “saute” and set it to high or “more”, then transfer the meat to your cutting board and shred it up.
Simmer the liquid that is in the pot for about 10-15 minutes or until it reduces by about half. Stir in the shredded chicken to soak up all of those juices. If still a lot of liquid remains, continue to simmer or press cancel.
If using spinach, add the spinach to a microwave safe bowl and microwave for 1-2 minutes, or until just thawed. Squeeze out as much excess water you can, then stir it into the chicken.