Preheat the oven to 425°F (220°C).
Toss the cubed sweet potatoes with 1 tablespoon of olive oil, half the salt, and a pinch of pepper. Spread on a baking sheet and roast for 20–25 minutes, until tender and lightly caramelized.
Meanwhile, pat the salmon dry. Rub with a little olive oil, the remaining salt, and pepper. Set aside until the potatoes are halfway done.
When the potatoes have about 10 minutes left, place the salmon on a separate lined sheet or pan. Bake for 8–12 minutes, depending on thickness, until the internal temperature reaches 145°F (63°C) and the flesh flakes easily.
While everything cooks, assemble the salad greens and red onion in a large bowl. If you like, drizzle a teaspoon of olive oil and a squeeze of lemon over the greens for a bright start.
Finish the chimichurri sauce or open a prepared jar. If you’re making it, mix chopped parsley, lemon zest and juice, a touch of salt, and enough olive oil to loosen it to a pourable consistency.
When the salmon is done, rest it for a minute or two. Slice if you prefer or flake it gently. Toss the warm sweet potatoes with a splash of lemon juice, then add to the greens along with the salmon and red onion.
Dress with chimichurri, toss lightly, and serve immediately. If you want extra brightness, squeeze a little more lemon over the top.