Soak. Place the dry porcini mushrooms in a bowl with 3 cups of hot water for 5 minutes. Reserve the stock.
Preheat the oven to 350 ºF (175ºC). Have ready a small oiled ovenproof dish.
Boil. Place the mushrooms, stock, and white wine in a medium saucepan and bring to boil.
Prepare onions:
Meanwhile, trim ¼ inch off the top and bottom of the onions.
Cut them lengthways in half and remove the brown skin.
Gently remove most of the insides (keep these for another use), retaining two or three of the outer layers.
Carefully separate the outer layers from each other and place them in the simmering stock, a few at a time. Cook for 3 to 4 minutes, or until just tender.
Drain well and cool slightly. Keep the stock.
Prepare the stuffing:
On a Medium Saucepan, melt the margarine or vegan butter and stir fry on medium heat the crumbled tofu, chopped drained porcini mushrooms, breadcrumbs, chopped spring onions, and garlic for 5 minutes.
Add ½ cup of white wine, followed by half of the resulting porcini/wine stock.
Add the chopped canned and dry tomatoes, quartered mushrooms, nutritional yeast, chopped parsley, salt, and pepper.
Cook for 10 minutes or until most of the liquid is absorbed.
Let it cool.
Assemble and bake:
Fill each onion layer generously with stuffing. Pull the sides together, so you end up with a fat cigar shape and secure them with a toothpick.
4 onions
Place the onions, seam-side down, in the oiled dish and pour over about ½ cup of the reserved stock, just to cover the bottom of the dish.
Bake for 45 to 50 minutes, or until de onions are soft and lightly colored, and the stuffing is bubbling; add more stock if they dry completely before the end of the cooking process. Serve warm.