1. Preheat your oven to 375°F (190°C).
2. Grease a 9×13-inch baking dish with cooking spray or butter.
3. In a large saucepan, bring the chicken broth to a boil.
4. Add the rice, reduce the heat to low, cover, and simmer for about 18 minutes or until the rice is tender and has absorbed all the liquid.
5. Fluff the rice with a fork and set aside.
6. Season the chicken pieces with salt and pepper.
7. In a large skillet over medium-high heat, cook the chicken until golden brown and cooked through (about 6–8 minutes). Remove from the skillet and set aside.
8. In the same skillet, sauté the onions until translucent (about 3–4 minutes).
9. Add the garlic to the skillet and cook for an additional minute until fragrant.
10. In a large saucepan, melt 1/4 cup of butter over medium heat.
11. Add the flour and whisk continuously for 1–2 minutes to create a roux.
12. Gradually pour in the milk, whisking constantly to prevent lumps from forming.
13. Continue cooking and whisking until the sauce thickens (about 5 minutes).
14. Remove the sauce from the heat and stir in 1 1/2 cups of shredded cheddar cheese until melted.
15. Add the thyme, oregano, salt, and pepper to taste.
16. In a large mixing bowl, combine the cooked rice, chicken, broccoli florets, sautéed onions and garlic, and the cheese sauce. Mix gently until all the ingredients are evenly coated.
17. Transfer the mixture to the prepared baking dish, spreading it out evenly.
18. In a small bowl, mix the crushed Ritz crackers or panko breadcrumbs with 2 tablespoons of melted butter.
19. Sprinkle the remaining 1/2 cup of shredded cheddar cheese over the casserole.
20. Top the casserole with the buttered cracker or breadcrumb mixture.
21. Bake the casserole for 25–30 minutes, or until it is bubbly and the topping is golden brown.
22. Remove the casserole from the oven and let it rest for 5–10 minutes before serving.
23. Garnish with fresh parsley if desired and serve hot.