Preheat your oven to 350°F (175°C).
In a large pot, cook the jumbo pasta shells according to package instructions until al dente. Drain and set aside.
In the same pot, add the broccoli florets to boiling water for about 2-3 minutes until just tender. Drain and set aside with the pasta.
In a skillet over medium heat, combine the cream cheese and milk, stirring until the cream cheese is melted and smooth.
Add the garlic powder, onion powder, salt, and pepper to the skillet, mixing well.
Stir in the shredded chicken and 1 ½ cups of cheddar cheese, mixing until well combined. Heat through for about 2-3 minutes.
In a mixing bowl, combine the cooked pasta, broccoli, and the chicken-cheese mixture. Gently fold until evenly coated.
Transfer the mixture into a greased baking dish. Top with the remaining ½ cup of cheddar cheese and breadcrumbs if using.
Bake in the preheated oven for 20 minutes or until bubbly and the top is golden brown.
Allow to cool for a few minutes before serving.