Preheat your oven to 375°F (190°C).
Prepare the chicken breasts by cutting a pocket into each piece.
Mix the Brie, cranberry sauce, thyme, and optional spinach in a bowl.
Stuff each chicken breast with the cheese mixture.
Season the stuffed chicken breasts with salt and pepper.
Heat olive oil in an oven-safe skillet over medium heat.
Sear each chicken breast for about 4-5 minutes per side until golden brown.
Transfer the skillet to the preheated oven and bake for 20-25 minutes.
Once cooked, let the chicken rest for 5 minutes before slicing.
Serve warm, garnished with additional thyme if desired.
