Pierce squash several times with a knife, creating holes to release steam.
Place whole squash in microwave-safe dish for 12 minutes, rotating halfway through, or until soft. Caution: squash will be hot.
Allow squash to cool slightly, then cut tops off the squash and split into two even halves. Remove the seeds.
Using a fork, scrape spaghetti strands from the inside of the squash into a colander.
Preheat oven to 400°F.
In a medium bowl, delicately combine turkey, bread crumbs, egg, cheese, carrot, zucchini, basil, parsley and garlic. Fold ingredients together using your hands; avoid over-mixing as meatballs could become tough.
Pour 1 cup spaghetti sauce into a 9x13-inch baking dish.
Roll your meatballs into approximately 1”-thick balls, and distribute evenly throughout baking dish.
Bake until meatballs have reached internal temperature of 165°F.
Combine spaghetti squash with remaining spaghetti sauce and meatballs and serve.