Preheat your oven to 375°F (190°C).
Using a sharp knife, carefully create a pocket in each chicken breast by slicing horizontally, being sure not to cut all the way through.
In a small bowl, mix together the brie cheese, cranberry sauce, and thyme. Season with salt and pepper.
Stuff each chicken breast pocket with the cranberry-brie mixture, dividing it evenly between the two breasts.
Secure the openings with toothpicks if necessary to keep the filling inside during cooking.
Heat the olive oil in an oven-safe skillet over medium-high heat. Once hot, add the stuffed chicken breasts and sear for about 3-4 minutes on each side until golden brown.
If using, mix breadcrumbs with melted butter and sprinkle over the chicken for a crispy topping.
Transfer the skillet to the preheated oven and bake for 20-25 minutes, or until the chicken is cooked through and reaches an internal temperature of 165°F (74°C).
Remove from the oven and let the chicken rest for 5 minutes before slicing.