For the dressing, roughly chop the garlic then pound to a paste in a mortar and pestle, with a pinch of sea salt.
Add the tahini to the pestle and mortar. Juice the lemon and add half of the juice to the pestle and mortar with the tahini and garlic. The mixture will thicken.
Add the remaining lemon juice and stir.
Add water, a tablespoon at a time, until the consistency is slightly thicker than you'd like the finished dressing to have. Add the olive oil and stir thoroughly - this should thin it to the desired consistency.
For the salad, place the chickpeas in a large bowl. Add the chopped onion.
Chop the tomatoes roughly and add to the bowl.
Add freshly ground black pepper and the parsley and coriander.
Drizzle some of the dressing over the salad and serve the rest alongside.
Sprinkle cayenne pepper, to taste, over the top and serve with warm pitta bread.