Sizzling Garlic Salmon with Sheet Pan Potatoes

Name: Sizzling Garlic Salmon with Sheet Pan Potatoes
Ingredients: 1 ½ pounds baby yellow potatoes, halved lengthwise; 1 large red onion, cut into 1/2-inch wedges; 5 spring onions (about 6 ounces), trimmed and halved lengthwise; ⅓ cup plus 2 tablespoons extra-virgin olive oil, divided; 2 teaspoons kosher salt, divided; ½ teaspoon black pepper, divided; ¼ cup Dijon mustard, divided; 1 (2-pound) skin-on or skinless salmon side; 3 garlic cloves, thinly sliced (about 1 1/2 tablespoons); 2 tablespoons chopped fresh tarragon; 2 tablespoons chopped fresh chives; Lemon wedges, for serving