Preparing the French Onion Chicken Bake is straightforward if you follow these simple steps:

1. Preheat Oven: Preheat your oven to 375°F (190°C).
2. Cook Onions: In a large skillet, heat olive oil over medium heat. Add sliced onions and cook until caramelized, about 15 minutes. Stir occasionally to prevent burning.
3. Season Chicken: While the onions are cooking, season the chicken breasts with garlic powder, thyme, salt, and pepper.
4. Brown Chicken: In another skillet, brown the chicken breasts over medium-high heat for about 3-4 minutes on each side. They do not need to be fully cooked, as they will finish in the oven.
5. Layer Ingredients: In a baking dish, spread the caramelized onions evenly at the bottom. Place the browned chicken breasts on top of the onions.
6. Prepare Sauce: In a bowl, combine beef broth and heavy cream. Pour this mixture over the chicken and onions in the baking dish.
7. Add Cheese: Sprinkle shredded Gruyère cheese generously over the top of the chicken.
8. Add Breadcrumbs: If using, sprinkle breadcrumbs over the cheese for extra texture.
9. Bake: Cover the baking dish with aluminum foil and bake in the preheated oven for 25 minutes. Then, remove the foil and bake for an additional 10-15 minutes, or until the chicken is cooked through and the cheese is bubbly and golden.
10. Garnish and Serve: Once baked, remove from the oven and let it rest for a few minutes. Garnish with fresh parsley before serving.

Following these steps will guide you in effortlessly creating this incredible dish.