In a large mixing bowl, combine the baby spinach, sliced cucumber, cherry tomatoes, red onion, and Kalamata olives.
In a separate small whisking bowl, combine the extra virgin olive oil, fresh lemon juice, dried oregano, salt, and black pepper.
Whisk the dressing vigorously until emulsified.
Drizzle the dressing over the salad components in the large bowl.
Gently toss the ingredients until the spinach leaves are evenly coated.
Top the salad with crumbled feta cheese and serve immediately.