Wash all vegetables under cool running water to remove dirt. Peel and slice cucumbers into thin rounds. Core and dice tomatoes. Slice red onion thinly. Place chopped ingredients in a large mixing bowl.

Slice the avocado in half, remove the pit, and scoop the flesh out with a spoon. Dice the avocado and gently fold it into the mixing bowl.

In a small bowl, whisk together olive oil and lemon juice. Season with salt and pepper to taste.

Drizzle the dressing over the salad and gently toss to combine, taking care not to mash the avocado.

Garnish with fresh herbs and adjust seasoning if necessary. Serve immediately or chill before serving.