1. Preheat your oven to 375°F (190°C). Line a baking dish with parchment paper or lightly grease it.
2. Start by preparing the mushroom filling. Heat 1 tablespoon of olive oil in a skillet over medium heat. Add the diced onion and sauté for about 3 minutes until translucent.
3. Add the minced garlic and chopped mushrooms to the skillet. Cook for 7-8 minutes, stirring occasionally, until the mushrooms release their moisture and begin to brown.
4. Pour in the chicken broth or white wine to deglaze the pan, scraping up any browned bits. Cook for another 2 minutes until the liquid reduces slightly.
5. Remove the skillet from heat. Stir in the Parmesan cheese, fresh parsley, thyme, salt, and pepper. Let the filling cool slightly before moving on.
6. Prepare the chicken breasts by placing them on a cutting board. Using a sharp knife, carefully slice a pocket into the thickest part of each breast, being careful not to cut all the way through.
7. Stuff each chicken breast with an equal amount of the mushroom mixture. If you’re using cheese, add a bit inside the pocket as well for extra creaminess.
8. Secure the opening with toothpicks if needed, to keep the filling inside during cooking.
9. Heat the remaining 1 tablespoon of olive oil in an oven-safe skillet over medium-high heat. Once hot, add the stuffed chicken breasts and sear for 3-4 minutes on each side until golden brown.
10. Transfer the skillet (or move the chicken breasts to the baking dish if your skillet isn’t oven-safe) to the preheated oven. Bake for 20-25 minutes, or until the chicken reaches an internal temperature of 165°F (74°C).
11. Optional: For a silky finish, melt a teaspoon of butter into the pan juices and spoon over the chicken before serving.
12. Let the chicken rest for 5 minutes before slicing. This helps the juices redistribute and keeps the meat tender.

I’ve found that searing the chicken first locks in the juices and gives you a beautiful golden crust that makes the dish feel extra special. It’s a trick I picked up from my grandmother, who always emphasized patience and attention to detail in the kitchen.