Preheat the oven: Preheat your oven to 375°F (190°C). Grease a 9×13-inch baking dish or line with parchment paper.
- Cook the chicken: Season the chicken breasts with salt and pepper. Heat olive oil in a large skillet over medium-high heat. Cook the chicken for 5-6 minutes per side, until golden brown and cooked through (internal temperature should reach 165°F or 74°C). Remove from the skillet and set aside.
- Prepare the broccoli: If using fresh broccoli, steam or blanch it for 3-4 minutes until tender. If using frozen, thaw and drain. Layer broccoli in the bottom of the prepared baking dish.
- Make the cheesy sauce: In a mixing bowl, combine shredded cheddar, cream cheese, sour cream, Parmesan, garlic powder, onion powder, thyme, and milk. Stir until smooth. Add more milk if the sauce is too thick.
- Assemble the bake: Place the cooked chicken on top of the broccoli. Pour the cheesy sauce over the chicken and broccoli, ensuring it’s evenly covered.
- Bake the casserole: Bake in the preheated oven for 20-25 minutes, until the cheese is bubbly and golden brown on top.
- Serve: Garnish with parsley if desired and serve with rice, quinoa, or a simple salad for a complete meal.