Begin by cutting the boneless, skinless chicken breast into bite-sized pieces for even cooking. Slice a mix of bell peppers and an onion if using.

Coat the chicken pieces with Cajun seasoning, ensuring each piece is well-covered. Let it marinate for 5-10 minutes.

Heat a large skillet over medium-high heat and add olive oil. Place the seasoned chicken into the skillet in a single layer. Cook for 6-8 minutes until golden brown and cooked through.

Remove the chicken from the skillet. In the same skillet, add the sliced bell peppers and onion. Sauté for 4-5 minutes until tender.

Return the chicken to the skillet with the sautéed vegetables. Toss everything together and sauté for an additional minute. Serve warm.