Preheat your oven to 375°F.

Line a large baking sheet with foil. Prep the squash as mentioned in Step 2 above. Brush 1 T of oil onto the inside of each spaghetti squash half. Season with the salt and pepper. Place the squash halves cut-side down on the baking sheet.

Roast the squash for about 45 minutes, or until it's fork-tender. The exact time may vary depending on the size of your squash, so keep an eye on it.

While the squash bakes, warm the remaining 1 tablespoon of olive oil in a large skillet over medium heat. Add the diced onion and cook until it softens. Stir in the minced garlic and sauté for 1 more minute until it's fragrant.

Add the ground beef to the skillet and break it up with a spoon as it cooks. Once it's fully browned, drain off any excess fat.

Pour the spaghetti sauce into the skillet with the beef, reserving 1 cup for later. Stir everything together, then cover and let it simmer on low heat for 10 minutes.

When the squash is done, carefully flip the halves over. Using a fork, scrape the inside of each squash to fluff up the "spaghetti" strands. Stir ¼ cup of the reserved spaghetti sauce into each half. Note: if your squash halves are becoming unwieldy and tipping over, transfer all of the strands to a lightly sprayed casserole dish and go to Step 8.

Sprinkle the parmesan cheese evenly and liberally over the squash in each half. Spoon the meat sauce on top, and then finish with a generous layer of mozzarella cheese.

Return the stuffed squash to the oven and bake at 375°F for another 15 minutes, or until the cheese is melted with golden edges.

Let the squash cool for a few minutes before serving hot.