Roasted Salmon with Mint-Caper Pesto

Preheat oven to 400°F with racks in upper and lower thirds. Coat 2 rimmed baking sheets with 1 tablespoon oil each. Divide shallots and scallions between sheets and drizzle each with 2 tablespoons oil; season generously with kosher salt and pepper. Roast, rotating pans and switching racks halfway through, until bottoms of alliums are golden brown, 25 to 30 minutes. Remove from oven; reduce temperature to 325°F. Let alliums cool, then consolidate on one sheet.

Place salmon on top of alliums on sheet. Brush with 2 tablespoons oil; season with kosher salt and pepper. Roast on lower rack until partially opaque in center, about 20 minutes.

Meanwhile, combine remaining 1/2 cup oil, mint, almonds, capers, 3/4 teaspoon kosher salt, and 1/2 teaspoon pepper in a mini food processor or blender, and purée until smooth.

Remove salmon and alliums from oven; carefully transfer to a serving platter. Sprinkle with flaky salt and serve with lemon wedges and pesto.