In a large bowl, combine tahini, lemon juice, and minced garlic. Mix well until a thick paste forms.
Gradually whisk in a few tablespoons of cold water until the dressing loosens to a creamy, pourable consistency similar to ranch or Caesar dressing.
Add the chopped tomatoes, cucumbers, bell pepper, red onion, and parsley to the bowl.
Mix gently until everything is evenly coated with the tahini dressing.
Season with salt and black pepper to taste.
Garnish with extra parsley and a sprinkle of sumac or chili flakes before serving.