Mix together the stock cube, soy sauce, tomato puree, worcestershire sauce, miso paste, mustard, barbecue sauce and boiling water in a large jug.
Heat the olive oil in a large pan and cook the onion, celery, carrot and garlic over a gentle heat for about 10 minutes until soft.
Add the nutritional yeast, mushroom powder, mixed herbs, smoked paprika, cumin, coriander, cayenne, garlic powder and plenty of black pepper. Add the ¼ teaspoon of salt only if you prefer a saltier meatloaf. Omit it if you are sensitive to salt. Cook for about 30 seconds while stirring
Add the wet ingredients and the TVP to the pan. Bring up to a simmer then remove from the heat and set aside for 20-30 minutes for the TVP to rehydrate.
Meanwhile, preheat the oven to 180°C/160°C fan/350°F/gas mark 4. Line a 2 lb loaf tin with baking parchment.
Stir the breadcrumbs and vital wheat gluten into the TVP mixture. Mix until no dry patches remain but do not knead the mixture.
Tip into the lined loaf tin and pack the mixture down evenly.
Cover with tin foil and bake for 1 - 1 ½ hours, until it no longer looks wet on top, a probe thermometer should register around 90℃/194℉ in the middle. Remove the tin foil, spread a layer of barbecue sauce over the top of the meatloaf and bake for 10-15 minutes more.