1. Preheat the oven to 425°F and line a baking sheet with parchment paper. Scoop and discard seeds from the squash. Drizzle the squash halves with olive oil and pinches of salt and pepper and roast cut-side up for 40 minutes, or until tender.
2. Cut the tempeh into 1/2-inch cubes, place in a steamer basket, and set over a pot filled with 1-inch of water. Bring the water to a simmer, cover, and let steam for 10 minutes. Remove, drain any excess water, and use your hands to crumble the tempeh.
3. Heat the olive oil in a large skillet. Add the onion,1/2 teaspoon salt, and several grinds of black pepper and cook 5 minutes. Add the mushrooms and cook, stirring, until soft, about 8 minutes. Stir in the crumbled tempeh, garlic, walnuts, tamari, apple cider vinegar, rosemary, and sage and cook 2 to 3 minutes more, adding 1/4 cup water as the pan gets dry. Stir in the cranberries and season to taste.
4. Scoop into the acorn squash halves and garnish with parsley and pomegranates.