In a blender, add 14 oz of Fire Roasted Tomatoes and 2 Chipotle peppers (in adobo sauce) and blend until smooth. Set aside.
Season 2 Chicken breasts with Salt and Pepper. Set aside.
Turn "Saute" on the InstantPot. Add 2 tbsp of Olive Oil and wait for it to heat up. Add a sliced medium Onion, a tsp of Minced Garlic, a Bay Leaf, 1/2 tsp of dried Oregano, a tsp of Cumin Powder and saute till golden brown.
Add 1/3 cup of Chicken Broth and deglaze. Add the chicken breasts, the tomato puree along with a tbsp of Adobo Sauce. Place the lid and set the steam release knob to "Sealing". Cancel the "Saute" option and set to "Manual Pressure" and cook for 8 minutes. After the timer is done, let it rest for 10 minutes. Quick release the pressure and open the lid.
Remove the chicken breast from the pot and shred using 2 forks. Add the shredded chicken to the pot and combine well. Adjust Salt and Pepper as needed.
Tacos - Heat the tortillas for 5 minutes. Add the Chicken Tinga to it. Layer with Avacado slices and shredded Cheddar cheese. Top it with a dollop of Sour Cream and serve.