Preheat your oven to 400°F (200°C). Toss the cubed butternut squash in a bowl with olive oil, salt, and pepper until evenly coated. Spread the squash on a baking sheet and roast for 20 minutes, or until tender and caramelized, stirring halfway through.

In a medium bowl, whisk together olive oil, maple syrup, apple cider vinegar, and Dijon mustard until well emulsified and creamy. Adjust seasoning as needed.

In a large bowl, combine mixed greens, roasted butternut squash, thinly sliced apple, dried cranberries, and chopped walnuts. Drizzle dressing over and toss gently until combined.

Transfer to a serving dish and sprinkle with feta cheese if desired. Serve immediately while the squash is still warm.