Start by adding your halved grape tomatoes, diced cucumber, rinsed chickpeas, diced green bell pepper, chopped parsley, and finely diced red onion to a large mixing bowl. Gently toss these ingredients together to distribute them evenly.
In a separate small bowl, whisk together the olive oil, red wine vinegar, cumin, salt, and black pepper. Continue whisking until the dressing is well combined and slightly emulsified.
Pour the prepared dressing over the vegetables and chickpeas in the large bowl. Toss everything together until the salad is thoroughly coated. For the best flavor, cover the bowl and refrigerate for at least one hour to allow the ingredients to marinate.
If you are using avocado, wait until just before serving to add it. Dice the avocado and place it in a small bowl, then squeeze the fresh lemon juice over it and stir gently. This prevents the avocado from browning. Fold the lemony avocado into the chilled salad.