In a medium bowl, combine tomatoes, cucumber, chickpeas, bell pepper, parsley, and red onion.
Add the olive oil, vinegar, cumin, salt, and pepper. Toss well to combine.
If using, cut the avocado into cubes and place in a small bowl. Squeeze the juice from ½ of a lemon over the avocado and gently stir to combine. (If not using avocado, squeeze 1 to 2 tablespoons lemon juice over the salad and toss.
Refrigerate for at least one hour before serving.
