Preheat oven to 400°F (200°C).
Toss diced sweet potatoes with olive oil, salt, and pepper.
Spread on a baking sheet and roast for 20-25 mins, flipping halfway, until tender and slightly crispy.
In a small bowl, whisk together maple syrup, Dijon mustard, apple cider vinegar, olive oil, salt, and pepper.
In a large bowl, combine mixed greens, roasted sweet potatoes, red onion, feta, walnuts, and cranberries.
Drizzle with dressing and toss gently.
Garnish with extra feta and walnuts if desired. Serve immediately.