Combine chickpeas, juice of 1 lemon and oregano in food processor. Mash garlic into paste with some salt pressing under the flat part of your knife then add garlic to processor along with tahini paste and parsley. Process hummus until smooth (add a splash of water if too thick) then transfer to a bowl and stir in olives, reserving a few for garnish. Serve dip with pita crisps and vegetable sticks.