Wash all vegetables thoroughly.
In a large bowl, add the mixed greens as the base.
Slice the cucumber and cherry tomatoes, then add them to the bowl.
Add the pitted black olives to the vegetable mixture.
Crumble the feta cheese and sprinkle it over the salad.
Thinly slice the red onion and add it to the bowl.
In a small bowl, whisk together olive oil, red wine vinegar, salt, and pepper.
Drizzle the dressing over the salad ingredients.
Gently toss the salad to combine all ingredients evenly.
Serve immediately or chill for 30 minutes to let flavors meld.