Preheat oven to 180 degrees C. Grease a glass baking dish. Cook the pasta according to packet directions then drain.
While pasta is boiling. Combine chicken, broccoli and cauliflower in a large bowl then set aside. In a saucepan melt the butter and onion. When onion is soft stir in the flour. Whisk in the milk then season to taste with salt, pepper and garlic. Remove from heat and stir in cheese.
When pasta is cooked, combine with the veggies. Stir in the cheese sauce. Pour into the prepared baking dish then top with breadcrumbs and extra cheese.
Cover with tinfoil then bake in preheated oven until chicken is cooked, about 30 minutes. Remove foil and cook until top is golden, about 5 minutes.
Just use what ever veggies and pasta you have on hand.