Place the cucumber, cherry tomatoes, red onion and chickpeas in a large mixing bowl. Set aside.
In a separate medium bowl whisk together balsamic vinegar, lemon juice, sugar, Italian seasoning, salt, black pepper and crushed red pepper flakes. Slowly drizzle in the olive oil in a steady stream whisking constantly.
Pour vinaigrette over the vegetables and gently toss to coat evenly. Cover and refrigerate for at least 2 hours.
Just before serving add the feta cheese, cubed avocado and Italian parsley to the marinated chickpeas and vegetables. Mix well, then taste and adjust the salt and black pepper to taste.