Carefully slice the spaghetti squash in half lengthwise and scoop out the seeds with a spoon.
Drizzle the inside of each half with olive oil, then season with garlic powder, onion powder, dried oregano, salt, and pepper.
Place the squash halves cut-side down on a baking sheet lined with parchment paper. Bake in the preheated oven for about 40-45 minutes, or until the flesh is fork-tender.
Once baked, let the squash cool for a few minutes, then use a fork to scrape the flesh into spaghetti-like strands.
Turn the oven down to 375°F (190°C).
In a mixing bowl, combine the scraped spaghetti squash strands with the marinara sauce and half of the mozzarella cheese. Mix until well combined.
Transfer the mixture back into the empty squash halves, spreading it evenly. Top each half with the remaining mozzarella cheese.
Bake for an additional 15-20 minutes, until the cheese is melted and bubbly.
Remove from the oven and let cool slightly before serving.
Garnish with fresh basil leaves and serve warm.
Notes
Feel free to add your favorite vegetables or proteins to the mixture.