In a large pot, bring 4 cups of water to a boil over high heat. Add 1 1/2 teaspoons salt, the pasta, and broccoli. Cook, stirring occasionally, for 8 minutes. Do not drain the water. Stir in the milk, cream cheese, and mustard, and cook until the cream cheese has melted and the pasta is al dente, about 4-5 minutes more. Stir in the zucchini.Add the cheeses, garlic powder, onion powder, paprika, cayenne, and butter (if using), and stir until melted and creamy. Remove from the heat. Season with salt and pepper. If the sauce feels thick, add ¼ cup milk or water to thin.Divide the mac and cheese between bowls. Top with black pepper.