Heat oven to 400° F. Toss the sweet potatoes with 2 tablespoons of the oil and ¼ teaspoon each salt and pepper on 2 rimmed baking sheets.
Roast, rotating the sheets and tossing the potatoes halfway through, until lightly browned and tender, 18 to 20 minutes. Let cool slightly.
Meanwhile, whisk together the lemon juice, mustard, the remaining 4 tablespoons of oil, and ¼ teaspoon each salt and pepper in a large bowl.
Add the kale and rub together with clean hands to tenderize and coat the leaves. Add the apple, almonds, and sweet potatoes and toss to combine.
Serve the salad topped with the shaved pecorino.