Cut the acorn squash in half and remove the seeds. Lightly coat with olive oil and season with salt. Place cut-side down on a parchment-lined baking sheet and bake for about 35-40 minutes, or until the squash is pierced easily with a fork.
Meanwhile, prepare the filling. Heat the olive oil in a medium pan over medium heat. Add the diced onions and cook until translucent. Next, add the sliced mushrooms. Season with salt and pepper and saute until browned. Add the minced garlic, tamari, and spices; cook for one more minute. Mix in the cooked wild rice, spinach, chopped nuts, and dried cranberries. Stir to wilt the spinach. Add salt and pepper to taste.
Remove the acorn squash from the oven and fill each with the wild rice mixture.