Make the seasoning. In a small bowl, combine chili powder, cumin, smoked paprika, garlic powder, onion powder, oregano, salt, black pepper, and cayenne.
Season. Toss the sliced chicken with 1 tablespoon oil and half the seasoning. In a separate bowl, toss the peppers and onions with the remaining oil and seasoning.
Preheat. Heat the Blackstone to medium-high (about 400–425°F) until a drop of water sizzles across the surface.
Cook the chicken. Spread the chicken in a single layer and sear undisturbed for 2–3 minutes, then stir and cook until it reaches 165°F internally, about 5–7 minutes total. Slide to a cooler zone.
Char the veggies. Add the peppers and onions to the hot zone and cook 4–6 minutes, stirring occasionally, until tender with charred edges.
Combine and finish. Toss the chicken back with the veggies, squeeze fresh lime juice over everything, and stir once more.
Serve. Warm the tortillas on the edge of the griddle for 20–30 seconds per side, fill with the fajita mixture, and add your favorite toppings.