1. Preheat oven to 350 degrees Fahrenheit.
2. Cut the butternut squash in half lengthwise. Scoop out and discard the seeds, then place squash onto a baking sheet, cut-side up. Brush with olive oil. Roast for one hour, or until squash is fork tender (timing may vary depending on size).
3. Let cool slightly, then scoop out the flesh in the center of the squash, leaving about a one-inch border all around. (I like to score a line an inch from the edge with the tip of my spoon before I start scooping so I have a guide to follow.) Chop the scooped squash flesh and set aside.
4. Grate cauliflower into a large bowl. Mix with reserved squash flesh, cranberries, celery, mint, parsley, scallions, sesame seeds, sunflower seeds, and pumpkin seeds.
5. Combine olive oil, lemon juice, sugar, salt, and pepper in a jar or airtight container and shake well. Pour over the salad and toss to coat.
6. Scoop as much tabbouleh salad as you can into the squash boats.
7. Pick up one squash half and flip it on top of the other. Use kitchen string to tie the squash in three to four places to hold it together.
8. To serve, slice into individual portions