Preheat oven to 425°F.

Using a serrated knife, slice each acorn squash lengthwise; remove seeds. (Tip: Acorn squash have very thick skins and a serrated knife makes it easier to cut the squash in half. If necessary, slice the lower half of each squash with the knife and then pry open with your fingers to snap the top apart.)

Place squash cut-side up on a baking sheet; brush the tops and insides of the squash with 2 Tbsp of olive oil. Sprinkle a small amount of salt and pepper on top of the squash and bake at 425°F for about 35-40 minutes, or until flesh is fork-tender.

Meanwhile, place the wild rice and chicken stock in a medium saucepan. Stir and bring to a boil over high heat. Once water begins to boil, reduce heat to low and cover pan with a tight-fitting lid. Simmer (without stirring) until rice has absorbed most of the stock (~30-40 minutes).

Place the remaining 2 Tbsp of olive oil in a large skillet and heat over medium heat. Add the onions, garlic and celery and sauté for 5-6 minutes. Add the ground beef, salt, pepper and oregano to the skillet. Continue cooking, stirring occasionally, until beef is fully cooked (~10-12 minutes).

Once rice has cooked, mix the rice, ground beef mixture and navy beans in a large bowl.

Reduce oven temperature to 325°F.

Fill the squash halves with the filling (~1 cup per squash half) and roast for another 15-18 minutes at 325°F.

Garnish with freshly grated Parmesan cheese prior to serving {optional}.