Heat the oven to 425° F
Oil a large rimmed baking sheet (half-sheet pan) or two smaller jelly roll pans.
Peel the butternut squash and, using a spoon, scoop out the seeds and fibers. Cut the squash into 1/2-inch cubes. Put about 4 cups of cubes into a large bowl.
Trim the stem ends off of the Brussels sprouts and removed loose, damaged, and yellow leaves. Cut the sprouts in half lengthwise. Add them to the bowl with the squash cubes.
Peel the onion and cut it into 1-inch chunks or thick slices. Add to the bowl with the squash and Brussels sprouts.
Drizzle the olive oil over the vegetables and gently toss or stir to coat them thoroughly with the oil.
Arrange the vegetables on the baking sheet and then sprinkle lightly with kosher salt, pepper, and garlic powder, if using.
Bake in the preheated oven for about 10 minutes and then turn the vegetables. Continue baking for 10 to 15 minutes longer, or until the vegetables are browned around the edges and are tender.
Meanwhile, toast the pecan halves. Heat a large dry skillet over medium heat. Add the pecans and cook, stirring, until the pecans begin to brown and smell aromatic.
Transfer the roasted vegetables to a large bowl. Add the dried cranberries and pecan halves and toss gently to combine all ingredients thoroughly.
Serve immediately.
