1. Preheat your oven to 375°F (190°C). While it warms up, line a baking dish with foil for easy cleanup.
2. In a skillet over medium heat, add the olive oil. Once hot, sauté the mushrooms, onion, and garlic until the mushrooms are golden and the onions are translucent, about 5-7 minutes.
3. Transfer the mushroom mixture to a bowl. Stir in the Parmesan, breadcrumbs, thyme, salt, and pepper. Mix until well combined.
4. Using a sharp knife, carefully cut a pocket into each chicken breast, being cautious not to slice all the way through.
5. Spoon the mushroom mixture into each pocket, securing them with toothpicks if necessary. This step always reminds me of the careful patience my dad showed when perfecting his dishes.
6. In the same skillet, melt the butter over medium-high heat. Sear each chicken breast for about 2-3 minutes per side, until golden brown.
7. Place the seared chicken breasts into the prepared baking dish. Pour the chicken broth over the top to keep them moist during baking.
8. Bake in the preheated oven for 25-30 minutes, or until the chicken is cooked through and juices run clear.
9. Remove from the oven, let rest for 5 minutes, then garnish with fresh parsley before serving.

As you follow these steps, remember that cooking is about love, not perfection. Embrace the mess and enjoy the process!