Bring a medium pot of water to a rolling boil. Add the couscous and continue to let it boil for 5-7 minutes, or until the couscous is tender. Drain the couscous in a colander or wire mesh sieve (if the holes in the colander are too big). Rinse briefly with cool water to cool off the couscous, then allow to drain while you prepare the rest of the salad.
Cut the cucumber into quarter rounds and place them in a large bowl. Take a big handful (or about 1/4 bunch) of parsley and pull the leaves from the stems. Roughly chop the parsley and then add it to the bowl with the cucumber.
Use a fine holed cheese grater or a zester to remove the thin layer of yellow zest from the lemon and add it the bowl with the other ingredients.
Cut the lemon in half and squeeze the juice into a small bowl (you should get 2-3 tablespoons of juice). Add the olive oil, garlic powder, salt, and some freshly cracked pepper.
Stir to combine and then pour the dressing over the cucumber, parsley, and lemon zest. Stir to combine.
Add the cooled and drained couscous and crumbled feta to the bowl. Gently stir to combine all of the ingredients. Taste and adjust the salt and pepper as needed. Serve immediately or chill until ready to eat.