PREHEAT oven to 350 degrees. Place spaghetti squash on a parchment paper lined baking sheet cut side down. Bake for 35-40 minutes. Remove from oven and cool 15 minutes.
WHILE squash cools, heat a medium skillet over medium heat and grease with olive oil spray. season chicken with sea salt, black pepper and dried basil on both sides. Place on skillet and cook 8-10 minutes each side.
WHILE chicken cooks, combine ingredients for walnut pesto in a blender or food processor and pulse until well combined.
SCRAPE spaghetti squash with a fork to remove strands into a large bowl. Toss with pesto. Thinly slice chicken and serve on top of spaghetti squash.