Preheat the oven to 400°F. On a large baking sheet, place the two spaghetti squash halves cut-side down and roast for 1 hour.
While the squash is roasting, in a large skillet over medium heat, heat the olive oil.
Sauté the onion and garlic until the onion is slightly translucent, about 5 minutes.
Add the ground beef, and break it apart with a wooden spoon.
Cook until no longer pink, 7 to 8 minutes.
Add the tomatoes, parsley, basil, and oregano, season with salt and pepper, and simmer on low until the squash has finished cooking.
Remove the squash from the oven, and let it cool for a couple of minutes. Rake the flesh out with a fork (you may need to wear an oven mitt on your other hand to steady the squash), and put the “noodles” in a serving bowl.
Top with the sauce, garnish with the extra parsley, and serve.