With the rack in the middle position, preheat the oven to 375°F (190°C). Line a baking sheet with parchment paper.
On a work surface, cut the squash in half lengthwise and remove the seeds. Season with salt and pepper. Place on the sheet, cut side down, and cook for 45 minutes to 1 hour or until the squash is tender. Let cool.
Shred the flesh with a fork.
In a bowl, combine the squash with 2 tbsp (30 ml) of the oil. Season with salt and pepper. Keep warm.
Meanwhile, in a skillet, brown the onions in the remaining oil. Season with salt and pepper. Add the garlic and cook for 1 minute. Add the broth, tomatoes and olives. Cover and simmer for about 5 minutes or until the tomatoes have slightly broken down. Remove from the heat. Add the cheese. Adjust the seasoning. Serve on a bed of spaghetti squash and sprinkle with the basil.
Recipes with the "Healthy Pick" stamp have been evaluated by a registered dietitian member of the Ordre professionnel des diététistes du Québec.