Make the sheet pan salmon: Preheat the oven to 425ºF.

Line a baking sheet with foil.

Put the potatoes and Broccolini in a large bowl, drizzle with 2 tablespoons of the olive oil, and season with salt and pepper.

Pour onto the prepared baking sheet in an even layer and roast for 15 minutes.

Meanwhile, drizzle the salmon with the remaining 2 tablespoons olive oil and season with salt and pepper.

Add the salmon to the baking sheet with the potatoes and roast until the potatoes are tender and the salmon is almost cooked, 5 to 7 minutes more.

Meanwhile, make the lemon-dill dressing: In a medium bowl, combine the lemon juice, mustard, olive oil, dill, and garlic and season with salt and pepper.

Set aside until ready to use.

Turn the oven to broil and brush the salmon and Broccolini with the lemon-dill dressing.

Broil for 2 to 3 minutes, until the Broccolini is charred and the potatoes are crispy.

Remove from the oven and serve.