Bring a pot of salted water to a rolling boil. Add the couscous, and stir. Cook for 5-7 minutes, or until it's tender but not mushy.
Pour the couscous into a strainer and run under cold water to stop the cooking process. Stir until cooled throughout, and set the couscous aside to drain.
Slice the cucumber into 1/4" coins. Quarter each coin, and add them to a large mixing bowl. Chop the parsley and add it to the bowl, along with the lemon zest & couscous. Gently toss everything to combine.
In a small bowl, whisk together the juice from the lemon, olive oil, mayo, garlic powder, salt & pepper until smooth.
Pour the dressing over the salad, and toss until everything's well coated.
Stir in the feta cheese. Taste the pasta. Season with additional salt & pepper, if desired.
Serve & enjoy!