Preheat your oven to 400°F (200°C) and line a large baking sheet with parchment paper.
Carefully slice the spaghetti squash in half lengthwise and use a spoon to scoop out and discard the seeds.
Brush the cut sides of the squash with half of the olive oil and sprinkle with a pinch of the sea salt.
Place the squash halves cut-side down on the prepared baking sheet and roast for 40 to 50 minutes until the skin is easily pierced with a fork.
While the squash is roasting, heat the remaining olive oil in a large skillet over medium-high heat.
Add the diced yellow onion to the skillet and sauté for 3 to 4 minutes until it becomes translucent.
Add the ground turkey to the skillet, breaking it into small crumbles with a spatula, and cook until no longer pink.
Stir in the minced garlic, dried oregano, remaining sea salt, and black pepper, cooking for 1 minute until fragrant.
Pour in the marinara sauce and bring the mixture to a gentle simmer for about 5 minutes.
Add the fresh baby spinach to the skillet and stir constantly until the leaves are just wilted.
Once the squash is finished roasting, use a fork to scrape the flesh into long, spaghetti-like strands.
Transfer the squash strands into the skillet with the turkey and sauce, tossing thoroughly to combine.
Garnish the dish with fresh chopped basil and serve immediately.