Wash mixed greens thoroughly and spin dry. Dice avocado, slice cucumber diagonally, and halve cherry tomatoes. Thinly slice red onion and soak in cold water for 10 minutes, then drain.

In a large bowl, combine mixed greens, diced avocado, halved cherry tomatoes, sliced cucumber, and soaked red onion.

Sprinkle crumbled feta cheese over the salad.

Whisk together olive oil and lemon juice in a small bowl, adding salt and pepper to taste.

Drizzle dressing over the salad and gently toss using tongs.

Serve immediately in bowls or on a platter.