1 (1-pound) butternut squash, trimmed and cut into (1-inch-thick) slices
1 (12-ounce) celery root, trimmed and cut into (1-inch-thick) slices
1 large Granny Smith apple (about 7 ounces), cored and cut into (1-inch-thick) slices
1 large carrot, peeled
1/2 teaspoon kosher salt, divided
2 tablespoons cider vinegar
2 tablespoons sparkling apple cider
1/2 teaspoon honey
6 tablespoons grapeseed or canola oil
4 cups trimmed arugula leaves
1/2 teaspoon freshly ground black pepper