- 1 medium delicata squash (12-14 ounces), halved, seeded, cut into 3/4" cubes
- 2 tablespoons plus 1/3 cup olive oil
- Kosher salt and freshly ground black pepper
- 1 cup skinned hazelnuts
- 1/2 cup hazelnut oil
- 1/2 cup Sherry vinegar
- 2 teaspoons sugar
- 1 6-7-ounce bunch mustard greens, center ribs and stems removed from tough greens, cut into 2" pieces (about 5 cups)
Place racks in top and bottom thirds of oven; preheat to 400°F. Line a rimmed baking sheet with foil. Toss squash with 2 tablespoons olive oil in a medium bowl; season to taste with salt and pepper. Spread out squash on prepared sheet and roast, turning occasionally, until tender and golden in spots, 18–20 minutes.
Meanwhile, spread out hazelnuts on a small rimmed baking sheet and toast in oven until beginning to turn golden brown, 8–10 minutes. Let cool on sheet.
Chop hazelnuts; place in a small bowl. Whisk in remaining 1/3 cup olive oil, hazelnut oil, vinegar, and sugar. Season vinaigrette to taste with salt and pepper.
Place roasted squash and mustard greens in a large bowl; toss to combine. Drizzle vinaigrette over and season with salt and pepper; toss to coat.