Put the broth and couscous into a medium saucepan and bring to a boil. Remove from the heat and set aside 5 minutes, until the broth is absorbed. Transfer the couscous to a bowl and cool. When cool, break apart the lumps with your fingers.
Add the tomato, green onions, cucumber, parsley and feta to the couscous.
Put the lemon juice, olive oil, oregano, salt, pepper and cayenne into a small jar. Cover and shake well to blend. Pour over the salad, mixing well.
Refrigerate; bring the salad to room temperature before serving.