Slice the zucchinis into quarters lengthwise, then slice thinly. A drum slicer with a mandolin blade works perfectly. Halve the cucumber lengthwise and scoop out the seeds with a spoon. Dice the rest of the cucumber. Combine the zucchini, cucumber, onion, tomatoes, olives, and feta cheese in a large bowl.
In a separate bowl, combine the olive oil, lemon juice, oregano, and a small amount of salt & pepper. Whisk the mixture until it's smooth. Toss the mixture with the rest of the salad. Marinate in refrigerator for 10 to 15 minutes.
Serve with a slotted spoon or drain before serving.
Store leftovers over a paper towel to absorb moisture.
Enjoy!