Tahini is sort of like peanut butter made from sesame seed and it's used a lot in Mid East baking and cooking (check out tahini and chocolate cake etc). You should be able to get it from any supermarket.
Trick is tahini, too little and it's chickpea rubble, too much it's like glue. Add a tbsp at a time and test in between until you're happy. Keep lemon juice on hand to break it up. Finish with additional olive oil (extra virgin only).