Using a pressure cooker:
With the pressure cooker's lid off, heat oil on HIGH or “brown” until sizzling.
Place onion, bell pepper, and jalapeno pepper in sizzling oil and sauté until onion is translucent.
Add lime juice, chili powder, brown sugar, salt, salsa and chicken stock to onion mixture and stir together.
Add chicken breast to cooker, securely lock the lid and set for 12 minutes on HIGH.
let the pressure cooker's pressure release naturally for 15 minutes before performing a quick release to release any remaining pressure.
Using a fork, shred the cooked chicken into the sauce in the cooker.
Assemble tacos by filling shells with lettuce, tomatoes, cheese and shredded chicken.