1) In a medium saucepan, add stock, orange zest, butter and salt to combine.
2) Place over high heat and bring a boil.
3) Stir in couscous, cover with a lid and remove from heat.
4) Allow the couscous to stand for 5 minutes.
5) Spread orange flower water over the couscous and sprinkle the pistachios.
6) With a fork, fluff the couscous lightly.
7) Transfer to a serving plate and serve warm by garnishing with fresh orange slices, if desired.