Cut the 2 lbs chicken breast into 1-inch chunks. Place the chicken in a zip-top bag with 1 tbsp olive oil and 2 tbsp Cajun seasoning. Seal the bag and massage it so all pieces are evenly coated. Let the chicken marinate for at least 10 minutes while you prepare the vegetables.

Core and seed the 2 bell peppers (1 red, 1 green) and cut them into bite-sized pieces. Press the 3 cloves garlic and chop the green onion to make 1/4 cup; set both aside.

Heat a large skillet over medium-high to high heat. Add the remaining 1 tbsp olive oil and heat until shimmering.

Add the chicken and the chopped bell peppers to the skillet in a single layer. If they cannot fit in a single layer, cook in batches to avoid overcrowding.

Cook the chicken and peppers without stirring for 3–4 minutes to brown the first side.

Use tongs to flip each chicken piece and continue cooking for 2 minutes on the second side.

Add the pressed garlic, stir to combine, and cook for 1 additional minute, or until the chicken reaches an internal temperature of 165°F and the peppers are tender-crisp.

Remove the skillet from the heat, sprinkle the chopped green onion over the chicken, and serve immediately.