Place each chicken breast on a cutting board and use a sharp knife to slice horizontally through the thickest part. Be careful not to cut all the way through, as you want to create a pocket for the filling. Season both the inside and outside of the chicken with salt, pepper, thyme, and smoked paprika.
In a medium skillet, heat one tablespoon of olive oil over medium heat. Add the minced garlic and cook for about 30 seconds until fragrant. Add the fresh spinach and cook until just wilted, which should take about 2 minutes. Remove from heat and let it cool slightly so it is easier to handle.
Open each chicken breast pocket and layer in a generous portion of the wilted spinach, followed by the dried cranberries and slices of Brie cheese. Do not overstuff, or the cheese will leak out too much during cooking. Secure the edges of the chicken with three to four toothpicks or tie them with kitchen twine to keep the filling tucked inside.
Wipe out the skillet used for the spinach and add the remaining tablespoon of olive oil over medium-high heat. Place the stuffed chicken breasts in the pan and sear for 3 to 4 minutes per side until they develop a beautiful golden-brown crust.
Preheat your oven to 375 degrees Fahrenheit. Transfer the seared chicken breasts to a baking dish or an oven-safe skillet. Bake for 15 to 20 minutes, or until the internal temperature of the chicken reaches 165 degrees Fahrenheit. Let the chicken rest for 5 minutes before removing the toothpicks and serving.
