Slice the chicken breast into thin, even strips and place them in a bowl.
Season the chicken with chili powder, cumin, garlic powder, sea salt, and black pepper, tossing to coat thoroughly.
Heat the avocado oil in a large cast-iron skillet over medium-high heat until it begins to shimmer.
Add the seasoned chicken strips to the skillet in a single layer and sear for 5-6 minutes until golden brown and fully cooked through.
Remove the chicken from the pan and set aside on a plate.
In the same skillet, add the sliced bell peppers and red onions, sautéing for 4-5 minutes until tender-crisp with slight charred edges.
Return the chicken to the skillet and pour in the lime juice, using a spatula to scrape up any flavorful browned bits from the bottom of the pan.
Toss everything together for one minute to combine the flavors.
Serve the fajita mixture topped with fresh cilantro and sliced avocado.