Place butternut squash in a medium saucepan; cover with water 2 inches above squash. Bring to a boil; cover, reduce heat, and cook 15 minutes or until tender. Drain.
Heat oil in a large nonstick skillet coated with cooking spray over medium-high heat. Add onion to pan; sauté 4 minutes or until tender. Add sage and next 4 ingredients (through red pepper); sauté 2 minutes. Cool.
Place squash, onion mixture, and sun-dried tomatoes in a food processor; process until smooth. Spoon into a medium bowl; sprinkle with pumpkinseed kernels.