The hummus can be made ahead; refrigerate, covered. Bring to room temperature (covered), then whisk with a touch of lemon juice or water before serving.
In the bowl of the food processor, puree the chickpeas and garlic clove. Stop and scrape down the bowl as you go, processing for several minutes until everything is completely smooth. This mixture may be very thick and ball up in the processor, depending how much liquid may be left in the cooked or canned chickpeas.
Add the tahini, lemon juice, and a pinch of salt. Process, taste, and add more salt or lemon juice to adjust texture and taste as needed.
Spoon the hummus onto a serving plate or bowl, making a well in the center with the back of a spoon. Fill the well with the chopped olives, then drizzle with olive oil. Serve immediately with veggies or pita chips or both!