Slice the chicken breast into thin strips and toss in a bowl with the chili powder, ground cumin, smoked paprika, sea salt, and black pepper.
Heat the olive 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, then remove from the pan.
In the same skillet, add the sliced bell peppers and red onion, sautéing for 4 to 5 minutes until they are tender-crisp with charred edges.
Return the chicken to the skillet, drizzle with the fresh lime juice, and toss everything together to combine the flavors.
Assemble the bowls by layering the warm cooked brown rice, the chicken and veggie mixture, sliced avocado, and a sprinkle of fresh cilantro.