Preheat oven to 400 degrees. Cut squash lengthwise in half. Remove seeds and rub oil on cut side, if desired. Sprinkle with salt and pepper. Roast cut side down on baking sheet for about 20 minutes or until tender.
In a medium sauce pan toast dry millet over medium heat for 4-5 minutes. Millet should be golden and fragrant. Add veggie stock, ¼ teaspoon salt, and bring to a boil. Reduce heat and cover. Simmer for 15 minutes or until most of water is absorbed. Keep covered and remove heat. Allow to rest for about 10 minutes to absorb remaining water and then fluff with a fork.
Toast walnuts in a dry pan for 4-5 minutes, if desired.
Heat 1 tablespoon of oil in skillet over medium heat. Sauté onion and apples until softened, about 5 minutes. Add kale and garlic and cook about 5 minutes longer or until kale is wilted and apples are easily pierced with fork. Add cooked millet, cinnamon, toasted walnuts if using, and raisins. Toss to combine and add additional salt and pepper if needed. Scoop filling into hollowed out squash and add a dash more cinnamon, if desired before serving.