Heat the oven: Preheat to 425°F (220°C). Line a rimmed sheet pan with parchment for easy cleanup.
Season the salmon: Pat the fillets dry. Brush with 1 tablespoon olive oil, then sprinkle with salt, pepper, and paprika.
Add lemon zest over the top for extra brightness.
Roast: Place salmon skin-side down on the sheet pan. Roast for 8–12 minutes, depending on thickness. It’s done when it flakes easily and the center is just turning opaque.
Aim for an internal temperature of 125–130°F for tender, medium doneness.
Sauté the garlic: While the salmon roasts, warm the remaining tablespoon of olive oil in a large skillet over medium heat. Add the garlic and cook for 30–45 seconds until fragrant, not brown.
Cook the spinach: Add the spinach in batches, tossing as it wilts. Season with a pinch of salt and red pepper flakes if using.
Cook 2–3 minutes until just wilted.
Finish the greens: Stir in the butter for a silky finish and squeeze in a bit of lemon. Taste and adjust salt.
Serve: Plate each salmon fillet with a mound of garlic spinach. Add a squeeze of lemon and a sprinkle of chopped parsley or dill.
Serve hot.