Preheat your oven to 375°F (190°C).
In a large skillet, heat the olive oil over medium heat. Add the sliced onions and sprinkle with salt. Cook, stirring occasionally, for about 15-20 minutes, or until the onions are caramelized and golden brown.
While the onions are cooking, season the chicken breasts with black pepper, garlic powder, and dried thyme.
In a large baking dish, pour the beef broth and place the seasoned chicken breasts in the dish.
Once the onions are caramelized, spread them evenly over the chicken.
Spoon the French onion dip over the onions and chicken, then sprinkle the shredded Swiss cheese and grated Parmesan cheese on top.
Cover the baking dish with aluminum foil and bake in the preheated oven for 25 minutes.
Remove the foil and bake for an additional 15-20 minutes, or until the chicken is cooked through and the cheese is bubbly and golden.
Remove from the oven and let it rest for 5 minutes before serving. Garnish with chopped parsley.