Step 1
Preheat the oven to 400 degrees F (200 degrees C). Line a baking sheet with parchment paper.
Step 2
Place each squash half cut-side down on the prepared baking sheet.
Step 3
Bake in the preheated oven until easily pierced with a knife about 45 minutes. Remove from oven and cool until easily handled. Scrape insides of squash into spaghetti strands with a fork. Transfer to a colander and place over a bowl to drain.
Step 4
While squash is baking heat olive oil in skillet over medium heat; stir in onion and garlic. Cook and stir until the onion has softened and turned translucent about 5 minutes. Add sausage breaking it up with a sturdy spoon to remove clumps. Cook and stir sausage in the hot skillet until browned and crumbly 5 to 7 minutes.
Step 5
Stir Worcestershire sauce Italian seasoning and 1 teaspoon salt into the sausage mixture. Add crushed tomatoes reduce heat to low and simmer for 30 minutes. Add wine and cook for another 30 minutes.
Step 6
Mix ricotta cheese Parmesan cheese basil leaves remaining 1 teaspoon salt and pepper together in a bowl.
Step 7
Layer 1/2 of the shredded spaghetti squash 1/2 of the ricotta mixture and 1/2 of the meat mixture in a 4-quart glass baking dish. Repeat layers once more and top with mozzarella cheese slices.
Step 8
Bake in the preheated oven turning halfway through until cheese is golden about 1 hour.
Step 9
Remove from the oven and immediately top with thin basil slices. Allow to cool for about 10 minutes before slicing and serving.