Preheat the oven to 400°F. Toss the cubed butternut squash with olive oil, salt, and pepper. Spread it on a baking sheet and roast for 25-30 minutes until tender and slightly caramelized.
While the squash is roasting, prepare the Brussels sprouts by trimming the ends and slicing them thinly.
In a large bowl, combine the mixed greens, roasted butternut squash, sliced Brussels sprouts, dried cranberries, toasted pecans, crumbled feta cheese, and red onion.
Drizzle the balsamic vinaigrette over the salad and toss gently to combine. Adjust seasoning with salt and pepper to taste.
Serve immediately or refrigerate for up to 30 minutes to allow the flavors to meld.