Preheat your oven to 400°F (200°C) and line a large baking sheet with parchment paper.
Peel the sweet potatoes and cut them into 1/2-inch cubes.
Toss the sweet potato cubes with half of the extra virgin olive oil and a pinch of sea salt on the baking sheet, then roast for 15 minutes.
While potatoes roast, mince the garlic, fresh dill, and fresh parsley.
Remove the baking sheet from the oven and move the potatoes to one side to make room for the salmon.
Place the salmon fillet on the sheet, drizzle with the remaining olive oil, and season with sea salt and black pepper.
Sprinkle half of the minced herb and garlic mixture over the salmon and top with thin slices from half of the lemon.
Return the pan to the oven and bake for 12-15 minutes until the salmon is opaque and the potatoes are tender.
Whisk the Greek yogurt with the remaining herbs and the juice from the other lemon half in a small bowl.
Remove the pan from the oven and immediately toss the baby spinach onto the hot baking sheet so it wilts slightly from the residual heat before serving with the herbed yogurt sauce.