Cut the butternut squash in half lengthwise and remove the seeds. Peel the pears, cut in half and remove the core. Place the pears and squash, cut side up, on a foil-lined baking sheet.
In a small saucepan, over low heat, melt the butter. Cut the vanilla bean in half lengthwise and scrape the seeds off of each side with a paring knife. Add the seeds to the butter. Reserve the pod for another use. Whisk the brown sugar and ginger into the melted butter and remove from the heat.
Brush the butter mixture onto the cut sides of the squash and pears. Season with salt and pepper. Set the remaining butter mixture aside and keep it warm. Roast the squash and pears until soft, about 45 minutes to 1 hour depending on the size of the squash. The squash is cooked when a knife can be inserted easily into the flesh.
Scoop flesh out of the squash and discard the skin. Place the squash and pears in a large bowl and mash with a fork or a potato masher. Stir in the remaining melted butter mixture. Season with salt and pepper, to taste, and serve warm.