Preheat oven to 190 degrees celsius (fan-forced).
Grease a casserole dish and set aside.
Place the quinoa, water and vegetable stock into a saucepan and cook for 15 minutes or until the liquid has disappeared. Fluff up with a fork and place into the prepared casserole dish.
Meanwhile, place the roughly chopped vegetables into the Thermomix bowl and finely chop on Speed 8 for 5-10 seconds (using the spatula to assist).
Remove the vegetables from the Thermomix bowl and strain any excess liquid away.
Place the finely chopped vegetables into the casserole dish with the cooked quinoa.
Place the cheese in to the Thermomix bowl and grate on Speed 10, 10 seconds. Set aside.
In a clean Thermomix bowl, place the butter, milk, plain flour, salt, pepper and half of the grated cheese and cook for 7 minutes, 80 degrees, Speed 4.
Pour the cheese sauce over the vegetables and quinoa and stir to combine.
Sprinkle over the remaining grated cheese.
Bake in the oven for 25-30 minutes or until the cheese is golden on top.