Place the garlic in a mini food processor, and process until finely chopped. Add the tahini, water and a pinch of salt. Process until smooth. Scrape down the sides, and add the yogurt, olive oil and lemon juice; process again until smooth. Season with salt to taste. Do Ahead: The yogurt tahini sauce can be made up to 3 days in advance. Store in a covered container in the refrigerator. Bring to room temperature before serving.