Preheat the oven to 400 degrees F (200 degrees C).
Peel butternut squash with a sharp vegetable peeler. Cut in half lengthwise; scoop out and discard seeds. Cut halves into 1-inch slices, then cut slices into 1-inch cubes.
Combine butternut squash cubes, olive oil, and garlic in a large bowl and toss until well coated. Season with salt and pepper. Arrange in a single layer on a baking sheet.
Roast in the preheated oven until squash is lightly browned and tender when pierced with a fork, 25 to 35 minutes.