- Bring large pot of lightly salted water to a boil. Add penne and stir occasionally to prevent sticking. Cook until just tender, about 10 minutes.
- Meanwhile, in large deep skillet, heat oil over medium heat. Add garlic and shallots and cook, stirring, until lightly browned, 2 minutes.
- Add zucchini and squash and cook, stirring occasionally, until tender and golden at edges, about 6 minutes.
- Drain penne, reserving 1 cup cooking water. Stir lemon peel, salt, pepper and reserved cooking water into Squash mixture.
- Transfer penne to large serving bowl. Add Squash mixture, basil and chives and toss to combine.
- Sprinkle with Parmesan cheese if using and serve hot.