Preheat your oven to 350°F (175°C).
In a skillet, heat olive oil over medium heat. Add the chicken breasts and season with salt, pepper, garlic powder, and onion powder. Sear the chicken for about 5-7 minutes on each side until browned and cooked through. Remove from heat and let cool slightly.
While the chicken is cooling, steam or blanch the broccoli florets and mushrooms for about 3-4 minutes until slightly tender. Drain well and set aside.
Once the chicken is cooled, cut it into bite-sized pieces and place it into a large mixing bowl. Add the steamed broccoli, mushrooms, shredded Swiss cheese, heavy cream, and chicken broth. Mix everything well until all ingredients are evenly coated.
Transfer the mixture into a greased 9x13 inch baking dish. Sprinkle additional Swiss cheese on top for an extra cheesy crust.
Bake in the preheated oven for 30-35 minutes, or until the casserole is bubbling and the cheese is melted and golden brown.
Once cooked, remove from the oven and let it rest for a few minutes. Garnish with fresh parsley if desired before serving.