Rinse the spinach under cold water and pat dry.

Slice the cherry tomatoes in half and dice the cucumber.

In a large mixing bowl, combine spinach, tomatoes, cucumber, and red onion.

In a small bowl, whisk together olive oil, lemon juice, salt, and pepper; drizzle over the salad.

Toss gently until everything is coated with dressing.

Top with crumbled feta cheese before serving.