- Preheat your oven to 400°F (200°C). 
- In a small bowl, mix together the Cajun seasoning, garlic powder, onion powder, smoked paprika, salt, black pepper, and cayenne pepper (if using). 
- Pat the chicken breasts dry with paper towels. Rub the spice mixture evenly over both sides of the chicken breasts. 
- In an oven-safe skillet, heat the olive oil over medium-high heat. Once hot, add the chicken breasts and sear for about 4-5 minutes on each side until golden brown. 
- Add the butter to the skillet, allowing it to melt and baste the chicken for an additional minute. 
- Transfer the skillet to the preheated oven and bake for 15-20 minutes, or until the chicken reaches an internal temperature of 165°F (75°C). 
- Remove the skillet from the oven and let the chicken rest for 5 minutes before slicing. Garnish with chopped green onions before serving.