Seared Salmon with Winter Vegetables and Kombu Broth

Name: Seared Salmon with Winter Vegetables and Kombu Broth
Ingredients: 2 tablespoons vegetable oil, divided; 1 small yellow onion, halved through root; 1 bunch small baby turnips (about 12 oz.), greens torn into pieces, turnips peeled, quartered; 3 large shallots, sliced into rings; 1 3” piece ginger, peeled, sliced ¼” thick; 3 oz. kombu; 1 tablespoon kosher salt, plus more; 1 cup dry vermouth; ½ small butternut squash (about 12 oz.), peeled, seeded, cut into ½”-thick pieces; 6 4-oz. pieces skin-on salmon fillet; Freshly ground black pepper; 1 lemon, halved