Turn the oven up to 425 F. While that's heating up, line a big, rimmed baking sheet with foil and, lightly spraying it with cooking spray.

In a medium bowl, toss the sweet potatoes with 2 teaspoons oil, 1/4 teaspoon salt, and 1/8 teaspoon pepper. Place the potatoes on half of the prepared baking sheet.

Bake the pan in the preheated oven for 5 minutes.

While that's baking, stir the Dijon, honey, and cayenne together in a small bowl. In a separate bowl, toss the broccoli with remaining oil, salt, and pepper.

Take the pan out of the oven and add the salmon to the other side of it. Brush the salmon with 2 teaspoons of the mustard mixture on each salmon filet, then sprinkle each evenly with bagel seasoning. Add the broccoli to the sweet potatoes. Put the pan back in the oven and bake until the salmon flakes easily with a fork and the veggies are golden, roughly 12 minutes.

Stir the soy sauce into the leftover mustard mixture and drizzle that over the vegetables.