Preheat the oven to 180°C.
Cook the pasta according to the packet instructions until just tender. Drain and set aside.
In a large bowl, combine the cooked chicken, pasta, broccoli, garlic, onion powder, cream of chicken soup, cream cheese, sour cream, grated cheese, Parmesan and lemon juice.
Season with salt and pepper and mix until everything is evenly coated in the creamy sauce.
Transfer the mixture to a large casserole dish and spread evenly.
Combine the crushed Ritz crackers with the melted butter.
Sprinkle the buttery cracker crumbs over the top of the casserole.
Bake uncovered at 180°C for approximately 25–30 minutes, or until piping hot throughout and the topping is golden.
Allow to sit for a few minutes before serving.