Preheat oven to 350 degrees F. Cut squash in half and arrange cut side down on a baking sheet. Bake for about 30 minutes, or until squash is tender. Dissolve brown sugar in melted butter. Brush squash with butter mixture and keep squash warm until stuffing is prepared. Heat olive oil in pan over medium heat. Sauté garlic, rainbow chard stems, and carrots together and cook for 5 minutes. Mix in garbanzo beans, cumin, pepper flakes and raisins. Continue to cook until vegetables are tender, seasoning with salt and pepper to taste. Pour chicken broth into the pan and mix in the uncooked couscous. Cover pan and turn off heat. The couscous will absorb the liquid in about 5 minutes. After liquid is absorbed, gently mix cilantro into couscous mixture. Stuff each squash half with the mixture and serve warm.