Preheat the oven to 400°F (200°C). Prepare a baking sheet with parchment paper.

Cut the spaghetti squash in half lengthwise and scoop out the seeds. Brush the insides with olive oil and sprinkle with salt and pepper.

Place the squash halves cut-side down on the baking sheet and roast for 30-40 minutes until tender.

In a skillet, heat olive oil over medium heat. Sauté onion and garlic until fragrant, about 3-4 minutes.

Add diced bell pepper and zucchini, cooking for an additional 4-5 minutes.

Stir in cooked ground turkey or chicken, Italian seasoning, salt, and pepper. Cook for 2-3 minutes.

Remove from heat and mix in marinara sauce.

Shred the roasted squash with a fork.

Combine shredded squash with the filling mixture in a large bowl.

Spoon the filling back into the squash halves and top with shredded mozzarella cheese.

Return to the oven and bake for an additional 10-15 minutes until cheese is melted and bubbly.

Serve and garnish with fresh basil if desired.