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 small bunch baby turnips (about 12 ounces), greens torn into pieces, turnips peeled, quartered; 3 large shallots, sliced into rings; 1 3 piece ginger, peeled, sliced 1/4 thick; 3 ounces kombu; 1 tablespoon kosher salt, plus more; 1 cup dry vermouth; 1/2 small butternut squash (about 12 ounces), peeled, seeded, cut into 1/2 thick pieces; 6 4-ounce pieces skin-on salmon fillet; Freshly ground black pepper; 1 lemon, halved