In a large saucepan, heat oil over medium heat. Add onions and leek; cook and stir until crisp-tender, 5 minutes. Add squash; cook and stir 5 minutes. Add garlic; cook and stir 1 minute longer. Stir in broth, thyme and salt. Bring to a boil. Reduce heat; cover and simmer until squash is tender, 15-20 minutes. , Discard thyme sprigs. Cool slightly. In a blender, process soup in batches until smooth. Return all to the pan. Stir in lemon juice and hot pepper sauce; heat through. Sprinkle each serving with cheese and lemon zest.