Preheat oven to 400 degrees F. Line 2 rimmed baking sheets with parchment.
Rinse the acorn squash, cut in half lengthwise, and remove seeds. Place acorn squash cut-sides down and slice into 3/4-inch-thick half-moons.
In a large bowl, whisk together the oil, vinegar and honey. Reserve half. Add squash to remaining balsamic mixture and toss to coat. Arrange squash on the baking sheets in a single layer. Season squash with salt and pepper.
Roast 15 minutes. Turn squash slices over. Roast another 15-25 minutes, until tender. During the last 5 minutes of cook time, sprinkle the pecans over squash to toast. To serve, drizzle with reserved balsamic mixture. Transfer squash and pecans to a serving platter.