Cook and drain pasta according to package directions.
Preheat oven to 400 degrees. Place chicken breast and broccoli onto an ungreased baking sheet. Season with salt and pepper. Bake 20 minutes. Remove from oven, but leave the oven on. Cut chicken into bite-sized pieces.
While the chicken and broccoli are cooking, make the mac and cheese: melt butter over medium-low heat in a large pot. Add garlic, flour, dry mustard, salt and pepper. Stir until the mixture starts to bubble.
Pour in the milk. Bring to a boil, stirring. Lower the heat to a simmer and stir in the cheese. Remove from heat.
Add the chicken, broccoli, pasta and herbs. Pour the entire mixture into a 9x13 baking dish. Bake 25 minutes at 400 degrees.