In a small bowl or jar, mix the basting liquid. Set aside.
Pause to preheat the oven to 400 F. (200 C.).
Add the oats to a food processor with a sharp blade. Blend the oats for a few minutes to break them down. Then add the mushroom powder, chickpeas, aquafaba, nutritional yeast, soy sauce, and vegetable broth. Blend until smooth.
In a medium mixing bowl, add the vital wheat gluten, garlic powder, onion powder, salt, and pepper. Mix well.
Make a well in the center of the dry ingredients and pour in the chickpea mixture. Stir with a wooden spoon until the dry ingredients are moist.
Use your hand to knead the dough in the bowl for 2 minutes and form a ball.
Lay a large piece of parchment paper or cling film on a flat surface. It should be larger than the bottom of your baking dish. Place the dough ball in the center of the parchment paper. Lay a piece of cling film (plastic wrap) as big as the parchment paper over the dough ball.
Use a rolling pin to form a rectangle a few inches longer than the length of your baking dish, about ½ inch thick.
Remove the top layer of cling film, then spread the dressing evenly over the top. Leave about 1 ½ inches around the edges of the dough free.
Adjust the parchment paper if necessary so the long side is in front of you. Roll the dough like a jelly roll.
Press along the edges to seal the length of the dough. Fold the remaining ends toward the long seal and press to secure them.
Add ¼ a cup of basting liquid to the bottom of the roasting dish. Then, carefully transfer the roast from the bottom parchment paper to the dish with the sealed side on the bottom. Brush more basting liquid over the top.