Heat the olive oil in a large frying pan and cook the celery for 1-2 mins just until softened. Add the chicken and fry for 7-10 mins until cooked through. Grate over the ginger, stir through the harissa to coat everything and cook for 1 min more.
Tip in the pienapple and quinoa, then pour over the stock and stir once. Cover with a lid or tightly cover the pan with foil and leave for about 5 mins until the quinoa has soaked up all the stock and is soft. Fluff up the quinoa with a fork and scatter over the coriander to serve. Serve with extra harissa, if you like.