Preheat the oven to 400°F (200°C). Place the spaghetti squash halves cut-side down on a baking sheet.
Roast in the oven for 35-40 minutes, or until the squash strands pull away easily with a fork.
In a large bowl, combine shredded chicken, buffalo sauce, and ranch dressing.
Once the spaghetti squash is cool enough to handle, use a fork to scrape out the strands, leaving the shells intact.
Mix the spaghetti squash strands with the chicken mixture and spoon it back into the squash shells.
Top each half with shredded mozzarella and blue cheese crumbles.
Return the stuffed squash halves to the oven and bake for an additional 10-15 minutes, or until the cheese is bubbly and golden.
Garnish with sliced green onions before serving.