Preheat the oven to 375°F (190°C), cut your squash in half (don’t try to cut through the stem, cut on one side of it), and scoop out the seeds.
Place the squash in a baking dish with the cut side face down, and add enough water to fill the baking dish by 1/4 of an inch. If using an 8x8 inch baking dish, that’s about 1 cup of water.
Loosely cover with foil and bake until totally soft, about 35 minutes. You want the skin to be soft as well because you can eat the skin.
Set aside the squash for now.
If you already have quinoa made, bonus. If not, you will need to cook 1/2 cup (90g) for this recipe. To do that, add the 1/2 cup of quinoa to 1 cup of water in a small pot, and bring to a boil. Turn the heat to low, stir and cover with a lid. Gently simmer for about 15 minutes, until all of the water is absorbed and the quinoa is soft and fluffy.
When the quinoa is done cooking, place it into a large mixing bowl and set aside for now.
Heat a large skillet over medium heat until the skillet is hot, about a minute. Add the onions and cook for 7 minutes, stirring often and adding just a splash of water as they start to stick. You want the onions to turn nice and brown, this will bring out the sweetness of the onions and give the overall dish a nice deep flavor. Add a splash of water each time you notice them sticking to the pan.
Add the mushrooms, celery, cabbage, salt, and pepper and cook for 5 minutes, stirring occasionally.
Add the veggie mixture and the lightly toasted walnuts to the quinoa and stir together.
Take each of the cooked squash halves and fill them with the quinoa mixture. Press the mixture down so that you can fit as much of the quinoa mixture in each half as possible.
Devour! Or share with friends at your holiday party :)