Press the "saute" function on your instant pot and add 2 tbsp olive oil. Add the onions and cook for 2-3 minutes or until translucent.
Stir in the garlic and cook for 5 seconds. Add the cumin, granulated garlic, onion powder, and oregano. Stir and cook for 30 seconds. Press the "cancel" function.
Remove the onion and garlic mixture from the instant pot and place it in a blender. Add the canned diced tomatoes and their juice, lime juice, chipotle sauce, and chipotle pepper. Blend until smooth.
Add the chicken stock to the instant pot and scrape the bottom. Place the chicken breasts in the instant pot and season the chicken breasts with salt. Pour the tomato and onion mixture over the chicken breasts and add the bay leaf. Do not stir!
Pop the lid on top, seal the valve, and pressure cook the chicken for 9 minutes.
Once the 9 minutes are up, do a quick release. Remove the chicken from the instant pot make sure to leave all of the sauce in the instant pot.
Shred the chicken using two forks or an electric mixer. Place the shredded chicken back into the instant pot and stir.
Press the "saute" function and cook for 1 minute. Check for seasoning and add more salt if needed. Enjoy on tostadas with cotija cheese, avocado, and lime, if desired.