Preheat the oven to 425°F (220°C). A high oven temperature gives the sweet potato a chance to caramelize and crisp the edges while cooking through, and it lets the salmon develop a lightly roasted exterior without overcooking the interior.

Prep the vegetables: scrub and dry the sweet potato; cut into 1/2-inch cubes (even size for even roasting). Pat broccoli florets dry and, if large, cut into bite-size pieces. Dry surfaces brown better—moisture prevents caramelization, so drying is essential.

Toss the sweet potato with 1 tablespoon olive oil, 1/2 tsp kosher salt, and a pinch of black pepper on a rimmed baking sheet. Spread into a single layer, leaving space between cubes—crowding creates steam instead of roast. Roast for 10 minutes before adding the broccoli so they finish at the same time.

After the first 10 minutes of roasting, remove the tray briefly and add the broccoli tossed with 1/2 tablespoon olive oil, 1/4 tsp kosher salt, and a pinch of pepper. Shake the pan so everything is in a single layer again and return to the oven for another 12–15 minutes, until the sweet potato is tender and browned at the edges and broccoli has bright green color with some charred tips. Staggering the timing ensures each vegetable reaches ideal doneness.

While the vegetables roast, make the lemon-herb dressing: in a small bowl combine the lemon zest, lemon juice (about 2 tablespoons), minced garlic, chopped rosemary or dill, and remaining 1/2 tablespoon olive oil. Whisk and season with remaining 1/4 tsp kosher salt and 1/4 tsp black pepper. The acid from lemon both seasons and 'cooks' the garlic slightly, mellowing its bite and marrying flavors.

Prepare the salmon: pat fillets dry with paper towels (key for good sear), then place skin-side down on a lightly oiled small baking sheet or ovenproof skillet. Brush the flesh with half of the lemon-herb dressing (reserving the rest for finishing). Season the flesh lightly if needed. Brushing before roasting adds flavor and helps protect the fish from drying out.

Bake the salmon at 425°F (220°C) for 8–12 minutes, depending on thickness. Cook until the flesh is just opaque and flakes when pressed with a fork; internal temp should be 125–130°F (52–54°C) for medium-rare to medium. A hot oven and short bake time give a tender, moist fillet with a lightly roasted surface.

When salmon is done, remove from oven and let rest 2 minutes (carryover heat finishes it). Toss the roasted sweet potato and broccoli in a large bowl with the remaining lemon-herb dressing so the hot vegetables absorb the flavors and the lemon brightens the natural sweetness.

Plate: divide the warm vegetables between two plates, place a salmon fillet on top, spoon any pan juices or remaining dressing over the fish, and finish with a few extra herb sprigs and a light grind of black pepper. The contrast of warm roasted vegetables with bright, acidic dressing and tender salmon creates a well-balanced, restaurant-quality plate.

Enjoy immediately. If you must reheat leftovers, do so gently in a 300°F (150°C) oven for 8–10 minutes to avoid drying the salmon.