Preheat your oven to 350°F (175°C) and line a baking sheet with parchment paper.

Mix together vital wheat gluten, chickpea flour, nutritional yeast, onion powder, garlic powder, poultry seasoning, thyme, and salt in a large bowl.

Combine vegetable broth, soy sauce, tomato paste, and olive oil in a separate bowl. Pour this mixture into the dry ingredients and knead for 3-4 minutes until a dough forms.

Prepare the stuffing by heating vegan butter in a pan. Sauté onion and celery until softened, then mix in sage, thyme, salt, pepper, cubed bread, and broth until everything is well-moistened.

Flatten the seitan dough into a rectangle. Place the stuffing in the center, then fold the edges over and seal completely.

Wrap the roast in parchment and foil, then place it on the prepared baking sheet. Bake for 60 minutes, flipping halfway through.

Whisk together maple syrup, balsamic vinegar, and Dijon mustard in a small bowl.

Unwrap the roast after the initial baking time. Brush it generously with the glaze and bake uncovered for an additional 15 minutes.

Rest the roast for 10 minutes after baking before slicing.