Bring chicken breast to a boil in a large saucepan and cook until internal temperature reaches 165 degrees (about 10 minutes). When done, carefully remove chicken, let cool and cut into bite-size chunks. Or use 3 cups leftover rotisserie chicken.
Prepare cooked white rice in a rice cooker or on the stove by following package cooking instructions.
Add broccoli to a large skillet with 1-2 cups of water. Cover and steam until fork-tender but still crisp (about 10 minutes). When done, drain and set aside.
Prepare the cheese sauce by adding butter to a saucepan over medium heat. Stir in flour and seasonings. Slowly stir in chicken broth and half and half. Continue to whisk until sauce lightly thickens. Melt in cream cheese and mustard. Remove from heat and stir in 1 ¾ cups cheese.
In a small bowl combine melted butter and crushed ritz crackers.
Prepare your casserole by lightly greasing a 9x13 baking dish. Gently stir together rice, broccoli and chicken in a large bowl. Pour in cheese sauce and stir to combine. Dump mixture into casserole dish. Sprinkle top with remaining cheddar cheese and ritz crackers.
Bake casserole uncovered for 35 minutes. When done, remove from the oven and let cool slightly before serving. Enjoy!