Preheat the Oven: Set your oven to 350°F (175°C).
Sear the Chicken: Season the chicken breasts with salt and pepper. In a large skillet, heat olive oil over medium heat. Brown the chicken on both sides, approximately 4-5 minutes per side. Once browned, remove and set aside.
Sauté Aromatics and Vegetables: In the same skillet, add chopped onion and minced garlic. Sauté until translucent, about 3 minutes. Add sliced mushrooms and broccoli florets; cook for another 5 minutes, stirring occasionally.
Incorporate Rice and Liquids: Stir in the long-grain rice, cooking for 2 minutes to allow it to absorb the flavors. Pour in chicken broth and heavy cream, stirring well to combine.
Combine and Bake: Return the browned chicken breasts to the skillet, ensuring they are well-covered with the rice mixture. Transfer the skillet to the preheated oven and bake for 25-30 minutes, or until the chicken is cooked through and the rice is tender.
Garnish and Serve: Garnish with fresh parsley before serving.