Dice your tomatoes. Then, peel and remove the extremities of your red onion. Slice it, using your Mandoline, on the thinnest setting. Do the same with the cucumber as well. Set aside.
Toss the baby spinach, tomatoes, red onion and cucumber with half of the dressing. Assemble the salad ingredients onto your serving platter. Sprinkle with Feta cheese and drizzle with the remaining dressing. Serve and enjoy. Bon Appétit!