Bring a pot of water to a boil. Add the couscous and continue to boil for about 5 minutes, or until the couscous is tender. Drain the couscous in a colander or wire strainer. Rinse briefly with cool water to cool off the couscous, then allow to drain while you prepare the rest of the salad.
Zest the lemon and then squeeze the juice. You'll need about ½ tsp of zest and 3 Tbsp of juice.
Add the lemon juice, olive oil, garlic powder, salt, and some freshly cracked pepper to a bowl and stir to combine.
Chop the cucumber into quarter-rounds and roughly chop the parsley.
Add the cooled and drained couscous to a large bowl along with the cucumber, parsley, lemon zest, and feta. Pour the dressing over top, then stir to combine. Serve immediately or refrigerate until ready to eat.
If you are substituting regular couscous for Israeli couscous, be aware that the cooking instructions are different. You can find instructions and step by step photos in this recipe post. You can substitute orzo for the couscous without any adjustments.