Preheat the oven to 425 degrees F (220 degrees C). Line a large, rimmed baking sheet with foil and coat lightly with cooking spray.

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

Bake in the preheated oven for 5 minutes.

While the potatoes are cooking, stir together Dijon, honey, and cayenne in a small bowl. Toss broccoli with remaining oil, salt, and pepper in a separate bowl.

Remove potatoes from the oven. Add salmon to the other half of the baking sheet. Place 2 teaspoons of the mustard mixture on each salmon filet; brush evenly to coat, then sprinkle evenly with bagel seasoning. Add broccoli to the sweet potatoes. Return to the oven and bake until salmon flakes easily with a fork and the veggies are golden, about 12 minutes.

Stir soy sauce into the remaining mustard mixture and drizzle over veggies.