Preheat your oven to 400°F (200°C). Carefully halve the spaghetti squash lengthwise and scoop out the seeds. Drizzle the cut sides with olive oil, then sprinkle with salt and pepper. Place cut-side down on a baking sheet lined with parchment paper and roast for 30-40 minutes until tender.

While the squash is roasting, heat a drizzle of olive oil in a skillet over medium heat. Add crumbled spicy Italian sausage and sliced mushrooms, cooking for about 5 minutes until browned. Drain excess fat if desired, then stir in minced garlic, Italian seasoning, and red pepper flakes. Add diced tomatoes and fresh spinach, cooking until the spinach is wilted.

Once the spaghetti squash is fork-tender, flip each half cut-side up on the baking sheet. Generously fill each half with the Italian sausage mixture, ensuring even distribution.

Top with halved cherry tomatoes and shredded Parmesan cheese. Return to the oven and bake for 15 minutes or until the cheese is melted. Broil for up to 3 minutes for a golden top. Garnish with fresh thyme before serving.