Preheat oven to 400°F (200°C). Toss the diced Butternut Squash with olive oil, salt, and pepper. Spread in a single layer on a baking sheet. Roast for 20-25 minutes, or until fork-tender and lightly caramelized. Reserve 1/2 cup of roasted squash for garnish, then mash the remaining squash until smooth.