Preparation
Preheat the oven to 375°F. Lightly coat a baking sheet with olive oil cooking spray.
Pierce the outside of each half of the squash a few times with a fork. Place the squash cut side down on the baking sheet and bake for about 45 minutes, or until very tender when tested with a fork. Cool slightly.
Meanwhile, place the avocado, basil or parsley, chives, Parmesan, garlic, salt, black pepper, and hot water in a blender and process until smooth, turning the blender off and on occasionally and adding a tablespoon or two of additional hot water if needed. There will be between ½ and ¾ cup of pesto.
When the squash has cooled, use a fork to rake the spaghetti-like threads of squash into a serving bowl. Discard the skin. There will be about 3 cups of spaghetti squash. Drizzle the pesto over the squash and garnish with fresh basil or parsley if desired.