Slice the chicken breast into thin, even strips and place them in a small bowl.
Toss the chicken with the chili powder, smoked paprika, ground cumin, sea salt, and black pepper until well coated.
Heat the avocado oil in a large cast-iron skillet over medium-high heat until shimmering.
Add the chicken strips to the skillet in a single layer and sear until golden brown and cooked through, about 5 to 6 minutes.
Remove the chicken from the skillet and set aside on a plate.
In the same skillet, add the sliced bell pepper and red onion, sautéing for 4 to 5 minutes until tender-crisp and slightly charred.
Return the chicken to the skillet, drizzle with fresh lime juice, and toss everything together for 1 minute to marry the flavors.
Garnish with sliced avocado and fresh cilantro before serving warm.