Slice a horizontal pocket into each chicken breast, being careful not to cut all the way through.
Season the chicken inside and out with salt and black pepper.
Stuff each chicken breast with apple slices and brie cheese. Add herbs if using.
Secure the opening with toothpicks if needed.
Heat olive oil and butter in a large skillet over medium heat.
Add stuffed chicken breasts and sear for 3–4 minutes per side until golden.
Reduce heat to low, cover, and cook for 8–10 minutes until chicken is fully cooked and cheese is melted.
Remove toothpicks and let chicken rest for 5 minutes before slicing and serving.