Puree quartered tomato, garlic, and half a can of chipotle peppers with adobo sauce and set aside.
Turn the Instant Pot to Saute mode and heat oil. Add sliced onions and cook for a minute with a glass lid on. Add diced tomatoes, chicken breasts, broth, and salt. Pour the pureed sauce over the chicken breasts. Pressure Cook for 8 minutes.
Allow 10 minutes of natural pressure release. Open the Instant Pot, take the chicken out, and shred it using two forks. Put the shredded chicken back in the pot and turn the Instant Pot to Saute mode. Cook for 5 mins or until the sauce thickens to the desired consistency. Adjust salt and add cayenne pepper to taste.
To serve: Cook the corn tortilla directly over medium flame until it gets a few charred marks. Serve with cabbage, red onions, cilantro, avocado, cheese, and a squeeze of fresh lime.