Put the brussels sprout on a tray with baking paper, add 1-2 teaspoons olive oil, a pinch of salt and mix it well.
Roast for 15 minutes, mix it again and then roast it for 15 more minutes (total of 30 minutes).
In the mean time, put the water in pot, add 1 teaspoon olive oil, a pinch of salt and bring it to boil. When the water boils, add the couscous, mix one time and remove it from the heat. Cover the pot with a lid and let it sit for 10 minutes.
Take a bowl, add the warm couscous, warm brussels sprout, walnuts, add some salt, olive oil and some chilli flakes on top. Mix it well and that is all.