Split the squash lengthwise and bake face-down in a 375 degree oven on an oiled tray, 30 minutes or until soft. Cool and scoop out the insides. Put it in the blender with the stock and puree until smooth. Combine in a saucepan with the orange juice. Heat the butter in a skillet and add the garlic, onion, salt, and spices. Saute until the onion is very soft. Add mushcooms, cover, and cook 10 minutes. Add the saute to the squash, scraping the skillet well to salvage all the good stuff. Heat everything together very gently. Taste to correct seasoning. You may want more cayenne or salt. And, since htis a is a fairly sweet soup, you may want to spruce it up with some fresh sqeueezed lemon juice. Squeeze into a seperate bowl so you don't get seeds. Serve topped with yogurt. This can simmer as long as you want-- no rush.