Add chicken breasts, salsa, and spices (cayenne pepper, salt, black pepper, garlic powder, ground cumin, chili powder, and dried oregano) to the Instant Pot.
Set Instant Pot to manual (high pressure) for 20 minutes. Let your Instant Pot do a natural release (aka let it sit for 10 minutes after the timer goes off), then quick release the pressure valve.
Shred chicken with a hand mixer or with two forks. Drain any excess liquid. Keep warm.
(optional step) Briefly toast tortillas in a pan heated over medium heat or in a toaster oven until light brown spots begin to show. Don't over-toast!
Assemble your toppings. Assemble each taco or serve family-style.
Notes
To make in a slow-cooker: Cook on high for 4 hours then shred, drain excess liquid, and serve.