Preheat your oven to 400°F and line a baking sheet with parchment paper.
Carefully halve the spaghetti squash lengthwise and use a spoon to scoop out the seeds and stringy bits.
Brush the interior of the squash with olive oil and sprinkle with half of the sea salt and black pepper.
Place the squash cut-side down on the baking sheet and roast for 40 to 45 minutes until the skin is easily pierced with a fork.
While the squash roasts, heat a large non-stick skillet over medium heat and add the diced yellow onion and minced garlic.
Sauté the aromatics for 3 minutes until translucent, then add the ground turkey to the skillet.
Cook the turkey, breaking it into small crumbles with a spatula, until it is fully browned and no longer pink.
Stir in the marinara sauce, dried oregano, and the remaining salt and pepper, then let the sauce simmer on low for 5 to 10 minutes.
Once the squash is done, let it cool slightly before using a fork to scrape the flesh into long, spaghetti-like strands.
Divide the squash strands onto plates, top with the hot turkey marinara sauce, and garnish with the grated parmesan cheese.