Position a rack in the center of the oven and preheat to 425 degrees F. Line a rimmed baking sheet with parchment paper. Lay the asparagus in the center of the prepared baking sheet, drizzle with 1 tablespoon olive oil and toss with 1/4 teaspoon salt and 1/8 teaspoon pepper. Roast until the asparagus just begins to change color, 5 minutes.
Remove the baking sheet from the oven and place the bok choy to the left of the asparagus. Drizzle with the remaining 1 tablespoon of olive oil and sprinkle with the grated ginger, 1/4 teaspoon salt and 1/8 teaspoon black pepper; toss to coat. Place the salmon fillets to the right of the asparagus, spacing them evenly apart. Brush with hoisin.
Roast until the bok choy is tender and the leaves begin to crisp, the asparagus is tender, and the salmon is cooked through yet still moist, about 12 minutes more. Divide salmon and vegetables between two plates and top with sliced scallions.
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