Position a rack in the center of the oven and heat the oven to 475° F. Line a heavy-duty rimmed baking sheet with parchment. In a medium bowl, toss the butternut squash with enough of the olive oil to coat generously, the salt, and a few grinds of pepper.
Turn the butternut squash out onto the baking sheet and arrange the pieces so that they are evenly spaced and lying on a cut side. If the pieces cover the baking sheet sparsely, arrange them toward the edges of the baking sheet for the best browning. Roast until the squash is browned on bottom, 15 minutes. Flip and roast until tender, 5 to 10 minutes.
Return the butternut squash to the bowl in which you tossed it with the oil, or put it in a clean serving bowl. If the squash seems a bit dry, drizzle it with a little oil. Season to taste with salt, pepper, and lemon juice, if using.