Preheat your oven to 200°C (390°F).
Use a sharp paring knife to carefully create a horizontal pocket in each chicken breast, slicing almost all the way through but keeping the sides intact.
Season the inside and outside of each chicken breast with salt, pepper, and chopped herbs for added flavor.
Mix the shredded cheese, sautéed spinach, chopped herbs, and optional bacon in a bowl, then stuff this mixture into each chicken pocket, pressing gently to fill them evenly.
Secure each stuffed breast with toothpicks or kitchen twine to prevent the filling from spilling out during cooking.
Heat olive oil or butter in a skillet over medium-high heat until shimmering and fragrant.
Place the stuffed chicken breasts in the skillet and brown for about 3-4 minutes per side until they develop a golden-brown crust and are nicely caramelized.
Transfer the skillet to the preheated oven and bake for 20-25 minutes, or until the internal temperature reaches 75°C (165°F) and the filling is bubbling.
Remove the chicken from the oven and let it rest for 5 minutes, allowing the juices to redistribute and the filling to set slightly.
Carefully remove the toothpicks or twine, then slice the chicken to reveal the gooey, cheesy center with a hint of green from the herbs.
Serve hot, accompanied by your favorite sides like roasted vegetables or a fresh salad, and enjoy the juicy, cheesy explosion with every bite.
