Preheat oven to 400 degrees. With a fork, prick squash in several places. Place on a rimmed baking sheet; bake until soft to the touch, about 1 hour.
When cool enough to handle, halve squash crosswise. Scoop out seeds; discard. Scrape flesh into strands.
In a large skillet, heat oil over low heat. Add garlic; cook until fragrant and just starting to color, about 5 minutes. Add squash; season with salt and pepper. Cook, tossing frequently, until squash is very hot, about 5 minutes.
Holding squash half over a wide bowl, use a fork to scrape the flesh into long, thin strands.