Preheat the oven to 375°F (190°C).

Using a sharp knife, create a pocket in each chicken breast by slicing horizontally, being careful not to cut all the way through.

In a bowl, combine the diced apple, cubed brie, and chopped thyme. Mix well.

Stuff each chicken breast pocket with the apple and brie mixture.

Secure the openings with toothpicks if necessary.

Rub the outside of the chicken breasts with olive oil, salt, and pepper.

Place the stuffed chicken breasts in a baking dish and bake for 25-30 minutes, or until the chicken is cooked through and juices run clear.

Remove the toothpicks, slice the chicken, and serve warm.