Delicata Squash with Orange and Pistachio

1 tablespoon extra-virgin olive oil
2 shallots, halved and sliced
1 large delicata squash, halved lengthwise, seeded and thinly sliced (about 4 cups)
1 teaspoon orange zest
3/4 cup orange juice
1/2 teaspoon salt
1/4 teaspoon freshly ground pepper
2 tablespoons chopped salted pistachios

Heat oil in a large nonstick skillet over medium heat. Add shallots and cook, stirring, until softened and beginning to brown, about 2 minutes. Add squash, orange zest and juice, salt and pepper. Reduce heat to medium-low, cover and cook, stirring once, until the squash is almost tender, 6 to 8 minutes. Uncover and cook, stirring occasionally, until the liquid is absorbed and the squash is tender and beginning to brown, 12 to 15 minutes more. Garnish with pistachios.