Preheat the oven to 450 F. Spray a rimmed baking sheet with nonstick spray (you can line it with foil or parchment paper first for easier cleanup).
Place the broccoli and potatoes on the baking sheet and drizzle with 2 tablespoons olive oil. Sprinkle over the garlic, red pepper flakes, salt, and pepper. Toss the mixture, then spread it out on the baking sheet in an even single layer. Roast for 20 minutes.
While the vegetables are roasting, rub the pink side salmon fillets with the remaining tablespoon of olive oil. Sprinkle with salt and pepper. Remove the tray from the oven, and nestle the salmon in between the vegetables. Return the tray to the oven and roast for another 10 minutes or so, until the vegetables are crisp in spots and tender and the salmon is cooked to your liking.
Divide amongst plates and serve with the lemon wedges, if desired.
Notes
Try this with other fish, like cod, halibut, or trout. If your fish filets are thinner than 1 inch, allow the vegetables to cook for 20 minutes instead of 15 before adding the fish filets.
Line the baking sheet with foil or parchment paper for easier cleanup.
Allowing the vegetables and potatoes to cook for a bit before adding the fish to the baking sheet means that everything will be cooked to perfection at the same time.
Try to keep everything in a single layer on the baking sheet so everything cooks evenly and gets nicely caramelized.