Preheat the oven to 400°F and line a 9x13-inch baking sheet with parchment paper.
Add the potatoes to the sheet pan and toss them with oil, salt, pepper, paprika, garlic powder, and onion powder until well coated. Roast for about 20 minutes, or until the potatoes start to soften and turn lightly golden.
While the potatoes are cooking, season the salmon with salt, pepper, and the remaining paprika, garlic powder, and onion powder, then set it aside.
In a small bowl, whisk together the maple syrup, Dijon mustard, lemon juice, red pepper flakes (if using), and salt to make the glaze.
Take the pan out of the oven and push the potatoes to one-third of the pan. Add the green beans and tomatoes to the center third, drizzle them with the remaining oil, season with the remaining salt and pepper, and toss to coat.
Place the salmon fillets on the final third of the pan and brush generously with the maple glaze, saving a little of the glaze for later.
Return the sheet pan to the oven and bake for 12–15 minutes, until the salmon flakes easily with a fork.
Brush the salmon with the remaining glaze, then broil for 1–2 minutes, watching closely so it doesn’t burn.
Finish with a sprinkle of fresh parsley and serve warm.