Preheat your oven to 375 degrees Fahrenheit and prepare the ingredients by slicing cremini mushrooms, dicing white onion and red bell pepper, and shredding pepper jack cheese.
Butterfly-cut the chicken breasts by making a horizontal cut, leaving one edge intact to create a pocket. Season with cajun seasoning and stuff with sliced mushrooms, diced onions, and red bell peppers. Add shredded pepper jack cheese and secure the pocket closed with toothpicks if needed.
Heat a skillet over medium-high heat and add olive oil. Once hot, sear the stuffed chicken breasts for about 5 minutes on each side until golden brown.
Transfer the chicken to a baking dish and bake in the oven for 20 minutes or until fully cooked. For an extra cheesy finish, top with additional shredded cheese during the last 5 minutes of baking.
Let the chicken rest for a few minutes before serving. Enjoy this showstopper dish with your choice of side dishes or as is for a flavorful and easy dinner experience.