Combine the smoked paprika, garlic powder, onion powder, oregano, cayenne, sea salt, and black pepper in a small bowl to create the Cajun spice blend.
Slice the chicken breast into thin, bite-sized strips and toss them in the spice mixture until every piece is thoroughly and evenly coated.
Heat the olive oil in a large non-stick skillet over medium-high heat until shimmering.
Add the chicken strips to the hot skillet and sear for approximately 5 to 7 minutes, turning occasionally, until the chicken is golden-brown and cooked through.
Remove the cooked chicken from the skillet and set it aside on a plate, keeping it warm.
In the same skillet, add the sliced bell peppers and red onion, sautéing for 4 to 5 minutes until the vegetables are tender yet still retain a slight crunch.
Return the chicken to the skillet and stir everything together for 1 minute to allow the flavors to meld and the chicken to reheat.
Serve the Cajun chicken and vegetable mixture immediately over the warm cooked brown rice.