Preheat the oven to 375°F (190°C).
Slice the chicken breasts lengthwise, creating a pocket for the filling.
In a bowl, mix the diced apples, Brie, walnuts, and thyme.
Stuff each chicken breast with the apple and Brie mixture, then season with salt and pepper.
Heat olive oil in an oven-safe skillet over medium heat. Sear the stuffed chicken for 5 minutes on each side.
Transfer the skillet to the preheated oven and bake for 25-30 minutes, or until the chicken is cooked through.
Remove from the oven and let rest for 5 minutes before slicing.
Serve warm, pair with your favorite side dish, and enjoy!