Arrange butternut squash in a single layer on a rimmed baking sheet; coat with cooking spray. Sprinkle evenly with salt and pepper. Bake at 425° for 15 minutes or until browned, stirring halfway through cooking.
Combine tahini paste, lemon juice, olive oil, and water in a small bowl, stirring with a whisk until smooth. Combine squash, pomegranate arils, and arugula in a large bowl; toss gently to combine. Drizzle squash mixture with tahini mixture.