Pierce spaghetti squash with a fork 10 times and place whole in a slow cooker. Cook on Low until very soft, about 4 hours. Halve squash and remove seeds.
Preheat oven to 400 degrees F (200 degrees C). Unroll pizza dough onto a greased baking sheet.
Scrape squash flesh into a bowl; mix in spaghetti sauce, ground beef, and zucchini. Spread squash mixture lengthwise down the middle of the dough. Top with cubed mozzarella cheese.
Cut sides of dough into even strips starting at the outside edges and stopping at the squash mixture. Fold alternating strips over squash mixture to form a braid. Brush with beaten egg and sprinkle with parsley.
Bake in the preheated oven until dough is brown and cheese is melted, about 30 minutes. Cool for 5 to 10 minutes before slicing.
If your spaghetti squash is too large for your slow cooker, pierce it with a fork and microwave whole for 5 minutes. The squash should then cut in half easily and fit into your slow cooker.
Spaghetti squash can also be cooked in the oven. Cut the squash in half, remove seeds, and drizzle with olive oil. Place cut-side down on a baking sheet and bake at 400 degrees F (200 degrees C) for 45 minutes.
You can substitute ground turkey, Italian sausage, or pepperoni for the ground beef, if you prefer.
Instead of greasing the baking sheet, you can use a sheet of parchment paper.
Per Serving: 483 calories;18.5 g fat;
53.3 g carbohydrates;
24.9 g protein;
81 mg cholesterol;
1176 mg sodium.