Slice the squash in half lengthwise, then use a large spoon to scoop out the seeds and stringy pulp. Place the squash in a roasting pan with the cut side down. Pour 2 cups of water into the roasting pan around the squash. Place the pan in the preheated oven and bake for 20 minutes.
In a medium saucepan brown the ground meat seasoned with salt and pepper. Pour off any excess fat to discard. Add the cumin, coriander, chipotles in adobo, garlic powder, oregano, and salsa and simmer for about 10 minutes.
When the squash has finished baking remove it from the oven and reduce the oven temperature to 350. Peel the skin off the squash, cut it into 1 inch cubes and place in a medium bowl. Pour melted butter over the squash and toss to coat. Season generously with salt and pepper to taste.
Spread the squash out in a 12 - 14 inch casserole dish. Sprinkle with 3/4 cup of shredded cheese. Spread the sour cream over the cheese layer. Spoon on the chili and spread it out, leaving a 1 inch border of spaghetti squash untouched around the edge. Top with the remaining 1 cup of shredded cheese. Bake in a 350 degree oven for 30 minutes or until heated through. Sprinkle with cilantro and serve with sides of sour cream, salsa, and guacamole or avocado slices as desired.
