START: In a large bowl, combine the adobo sauce with 1 teaspoon salt. Add the chicken and stir to coat. On a 6-quart Instant Pot, select More/High Sauté. Add the oil and heat until shimmering. Add the onion and cook, stirring occasionally, until softened, about 5 minutes. Stir in the garlic, cumin and chipotle chilies, then cook, stirring, until fragrant, about 1 minute. Add ½ cup water, scraping up any browned bits. Add the chicken, stir to combine, then distribute in an even layer. Scatter the tortillas evenly over the chicken. Pour the tomatoes over the top but do not stir.
FAST: Press Cancel, lock the lid in place and move the pressure valve to Sealing. Select Pressure Cook or Manual; make sure the pressure level is set to High. Set the cooking time for 8 minutes. When pressure cooking is complete, allow the pressure to reduce naturally for 15 minutes, then release the remaining steam by moving the pressure valve to Venting. Press Cancel, then carefully open the pot.
SLOW: With the pot still on More/High Sauté, bring the mixture to a boil. Press Cancel, lock the lid in place and move the pressure valve to Venting. Select Slow Cook and set the temperature to Less/Low. Set the cooking time for 4 to 5 hours; the chicken is done when a skewer inserted into the largest piece meets no resistance. Press Cancel, then carefully open the pot.
FINISH: Using a slotted spoon, transfer the chicken to a large bowl and let cool for about 5 minutes. Using two forks, shred the meat. Select More/High Sauté and bring the sauce mixture to a simmer. Cook, stirring often and scraping the bottom of the pot, until the sauce is very thick, 5 to 8 minutes. Press Cancel to turn off the pot. Return the chicken to the pot, add the cilantro and stir to combine. Taste and season with salt and pepper.
Tip: Don't use flour tortillas or tortillas made from a corn-flour blend as neither will break down properly to thicken the sauce. After pouring the tomatoes into the pot, don't stir them in because they have a tendency to stick and burn on the bottom of the pot.