Preheat oven to 400 degrees F. Slice off the hard end of the Brussels sprouts, before peelig off their outer layer of leaves and cutting them in half. Place sprouts on a baking tray with olive oil, salt, pepper and chili flakes, and bake for 30 minutes - until they begin to crisp and the very edges tun ever so slightly brown. While the sprouts cook, prepare the quinoa. Boil it in a saucepan of water with, 1 tablespoon apple cider vinegar and a sprinkling of salt. Allow the quinoa to simmer for about 30 minutes, until the grains are soft. The mushrooms will take about 8-10 minutes to saute so can be cooked last. Peel off their skin, remove the hard stalk from the middle and cut in half, before cutting each half again into thin slices. Place them in a frying pan with olive oil, salt and any dried herbs. Cook on a low to medium heat until soft and brown.