Preheat the oven to 400°F (200°C). Line a baking sheet with parchment paper.
- Toss the cubed butternut squash with olive oil, salt, and pepper. Spread evenly on the prepared baking sheet.
- Roast for 25-30 minutes, flipping halfway through, until tender and golden brown.
- Toast the walnuts in a dry skillet over medium heat for 5-7 minutes, until fragrant and lightly browned. Set aside.
- In a small bowl, whisk together Greek yogurt (or mayonnaise), apple cider vinegar, honey (or maple syrup), cinnamon, salt, and pepper for the dressing.
- In a large bowl, combine roasted squash, chopped apples, halved grapes, toasted walnuts, mixed greens, and celery. Add dried cranberries or raisins if desired.
- Toss with the dressing and serve immediately as a side dish or light main course.