Prepare the fajita seasoning by combining 2 teaspoons chili powder, 1 teaspoon ground cumin, 1 teaspoon smoked paprika, 1 teaspoon kosher salt, ½ teaspoon garlic powder, ½ teaspoon onion powder, and ⅛ teaspoon cayenne pepper in a small bowl.
Trim any fat from 2 pounds boneless skinless chicken breasts and then slice into ½-inch thick strips, lengthwise (long, thin strips). Sprinkle ½ the fajita seasoning mixture over the chicken and toss to coat evenly with the spice mixture.
Add the chicken stock to the inner pot, using ½ cup for a 3 or 6-quart Instant Pot or ¾ cup for an 8-quart model.
Add the seasoned chicken to the inner pot. Top with the 1 large yellow or white onion (sliced), 3 large bell peppers (sliced), and 3 cloves minced garlic. Sprinkle the remaining fajita seasoning over the pepper and onions.
Seal the instant pot, being sure the vent knob is pointed to sealed or the lid is locked. Using the pressure cook or manual button, set the cooking time to 4 minutes on High Pressure.
Once cooking time is finished, let the pressure release naturally for 10 minutes.
Using a slotted spoon, transfer the chicken, onions, and peppers from the inner pot to a serving bowl. Add the zest and juice of 2 medium limes and toss to coat.
Serve the fajita mixture as desired on warmed tortillas or over rice with your favorite toppings.