Cook the couscous: Bring a large pot of generously salted water to a boil. Add pearl couscous and cook according to package directions until al dente, about 8-10 minutes. Drain and rinse under cold running water until completely chilled.
Prepare the vegetables: While couscous is cooking, halve the cherry tomatoes, slice cucumbers, thinly slice red onion, cube feta cheese, and chop mint.
Make the vinaigrette: In a small bowl or measuring cup, whisk together the olive oil, apple cider vinegar, lime juice, Dijon mustard, oregano, minced garlic, salt, and pepper until well blended.
Assemble the salad: In a large serving bowl, combine the chilled couscous, prepared vegetables, feta cheese, olives, and mint. Pour the vinaigrette over the salad and toss gently until evenly coated.
Rest and serve: Refrigerate for at least 1 hour to allow flavors to meld. Serve chilled or at room temperature.