Making Mushroom Stuffed Chicken Breast is a straightforward process when you follow these steps:

1. Preheat Oven: Preheat your oven to 375°F (190°C).
2. Prepare Chicken: Use a sharp knife to create a pocket in each chicken breast. Be careful not to cut all the way through.
3. Cook the Filling: In a large skillet, heat olive oil over medium heat. Add the diced onion and cook until translucent, about 3-5 minutes.
4. Add Mushrooms: Stir in finely chopped mushrooms and cook until they release their moisture and begin to brown, around 5-7 minutes.
5. Mix Ingredients: Stir in minced garlic, dried thyme, salt, and pepper. Cook for another minute before removing from heat.
6. Combine with Cheese: In a bowl, mix the mushroom mixture with softened cream cheese and shredded mozzarella. Ensure the ingredients are combined well.
7. Stuff the Chicken: Fill each chicken breast pocket generously with the mushroom and cheese mixture. Secure the openings with toothpicks or kitchen twine.
8. Season: Season the outside of each chicken breast with salt and pepper to taste.
9. Bake: Place the stuffed chicken breasts in a baking dish and cover with foil. Bake for 20 minutes, then remove the foil and bake for an additional 10-15 minutes until the chicken is cooked through (internal temperature should reach 165°F or 74°C).
10. Rest: Once done, take the chicken out of the oven and let it rest for 5-10 minutes to allow the juices to redistribute.
11. Garnish: Remove toothpicks or twine before serving. Garnish with chopped fresh parsley for added freshness.

These straightforward steps will lead you to a delicious Mushroom Stuffed Chicken Breast that delights the senses!