Preheat your oven to 400°F (200°C) and line a baking sheet with parchment paper.
Toss the cubed sweet potatoes with half of the olive oil and a pinch of salt, then spread them in a single layer on the baking sheet.
Roast the sweet potatoes for 20-25 minutes, tossing halfway through, until they are tender and slightly browned.
Season the salmon fillet with salt and pepper on both sides.
Heat the remaining olive oil in a non-stick skillet over medium-high heat.
Place the salmon in the pan, skin-side down if applicable, and sear for 4-5 minutes until the skin is crisp.
Flip the salmon carefully and cook for another 2-3 minutes until it reaches your desired level of doneness, then remove from the pan to rest.
In the same skillet, add the minced garlic and sauté for 30 seconds until fragrant.
Add the fresh spinach to the skillet and toss constantly until just wilted, about 1-2 minutes.
Plate the salmon alongside the roasted sweet potatoes and sautéed spinach, finishing with a fresh squeeze of lemon juice over the fish and greens.