Preheat oven to 425°F. Line a large sheet pan with parchment.
Toss sweet potato cubes with olive oil, kosher salt, and pepper. Spread in a single layer.
Roast 22–28 minutes, flipping once, until tender with caramelized edges. Cool 5 minutes.
Whisk dressing: olive oil, cider vinegar, lemon juice, Dijon, maple syrup, garlic, salt, and pepper.
Massage chopped kale with 2 tablespoons dressing until softened, 30–60 seconds.
Add warm sweet potatoes, red onion, cranberries, and pecans. Drizzle on remaining dressing; toss well.
Fold in feta. Taste and adjust salt or lemon. Serve warm or at room temperature.