Preheat oven to 375 degrees F.  Cut the spaghetti squash in half lengthwise and scoop out all the seeds.  Brush with just a little olive oil (about a teaspoon) and sprinkle with salt and pepper.  Place both halves of the squash cut side down on a prepared baking sheet and bake in the oven for 35 to 40 minutes.

While the squash is roasting, drizzle oil into a large pan over medium heat and sauté the onion and garlic until fragrant, about 2 minutes. Add ground beef and cook until meat is browned and crumbled, draining if necessary.

Stir in seasonings and salt/pepper, then pour in the marinara and mix well until everything is combined.  Bring the sauce to a boil, then reduce the heat and let the sauce simmer for about 10 minutes.

Remove the squash from the oven and let cool for a few minutes until it's easier to handle then using a fork, scrape out all the insides and add to the sauce that's simmering on the stove.

Toss spaghetti squash with meat sauce and cook for about 3 more minutes, just so all those flavors can heat through.

Transfer spaghetti squash and meat sauce to a 9x13 casserole dish lightly coated with nonstick spray.  Top with shredded mozzarella cheese, layer pepperonis and sprinkle with additional Italian seasoning (and red pepper flakes), if desired.

Bake the pizza casserole in the oven, uncovered for about 25 minutes until hot and bubbly.  Serve and enjoy!