Preheat your oven to 400°F (200°C).
In a large bowl, toss the cubed butternut squash with olive oil, salt, black pepper, and ground cinnamon until evenly coated.
Spread the squash in a single layer on a baking sheet lined with parchment paper.
Roast in the preheated oven for about 25-30 minutes, or until the squash is tender and lightly caramelized, stirring halfway through.
While the squash is roasting, prepare the dressing by whisking together balsamic vinegar, maple syrup, and Dijon mustard in a small bowl.
In a large salad bowl, combine the mixed greens, sliced red onion, dried cranberries, and toasted walnuts.
Once the butternut squash is done roasting, allow it to cool slightly before adding it to the salad bowl.
Drizzle the dressing over the salad and toss gently to combine. If using, sprinkle the crumbled feta cheese on top before serving.