Preheat an oven then line a sheet pan with parchment. Using a large chef’s knife, cut each spaghetti squash in half lengthwise through the stem. Use a large spoon to scoop out the seeds. Drizzle the flesh of each squash with a little olive oil, then season.
Heat remaining olive oil in a large skillet over medium-high heat. When hot, add Italian sausage to the pan. Use a spatula to help break up the sausage into small pieces. Stir fresh baby spinach, chopped garlic, and a pinch of crushed red pepper flakes.
Carefully flip the squash over, then divide and spoon the filling into each half. Sprinkle with shredded Mozzarella cheese and grated Parmesan, dividing equally between each
Bake the stuffed squash until the cheese has melted. Finish with chopped fresh basil or parsley, freshly ground black pepper, and a pinch of flaky sea salt. Enjoy!