Cut squash in half lengthwise; discard seeds. Place squash on a microwave-safe plate, cut side down. Microwave, uncovered, on high 18-20 minutes or until tender.
In a large skillet, heat oil over medium heat. Add corn; cook and stir 5-7 minutes or until lightly toasted.
When squash is cool enough to handle, use a fork to separate strands; stir into skillet. Add black beans, salsa, onions, cilantro, pumpkin seeds, lime juice, garlic salt, cumin and salt; heat through. Serve with tortillas and, if desired, guacamole.