Creamy Ravioli With Squash, Lemon, and Chives

cheese ravioli (fresh or frozen)

olive oil

shallot, chopped

summer squash (zucchini and/or yellow squash; about 1 1⁄2 pounds), thinly sliced

kosher salt and black pepper

heavy cream

grated lemon zest

grated pecorino or Parmesan (2 ounces), plus more for serving

chopped fresh chives