On your Instant Pot®, select Sauté Low. When the display reads “Hot,” add the oil and heat until it shimmers. Add the onion. Cook for 1 minute, stirring. Add the sweet potato and bell pepper. Cook for 1 minute, stirring so nothing burns. Turn off the Instant Pot® and add the garlic. Cook for 30 seconds to 1 minute, stirring.
Add the tomato, black beans, chipotle, adobo sauce, chili powder, salt, cumin, stock, and lime juice. Lock the lid and turn the steam release handle to Sealing. Using the Manual function, set the cooker to High Pressure for 4 minutes (3 minutes at sea level).
When the cook time is complete, turn off the Instant Pot® and let the pressure release naturally for 5 minutes; quick release any remaining pressure.
Carefully remove the lid. If there is too much liquid in the inner pot, select Sauté Low again and cook for 1 to 2 minutes, stirring constantly (it gets hot fast!).
Stir in the lime zest. Serve in the tortillas, topped with mashed avocado and cilantro and anything else your heart desires.