Preheat a large pan, preferably cast iron, over medium heat.

Saute the shiitake mushrooms and leeks in olive oil until soft, about 10 minutes.

Add salt, pepper, minced garlic and chopped fresh thyme and cook for about 2 more minutes, stirring often.

Sprinkle in the breadcrumbs and toss to coat.

Cook the mushroom mixture, stirring very often, until the breadcrumbs are toasty and the mixture is relatively dry, about 5 minutes.

Drizzle in the vegetable broth and lemon juice and toss to coat until moist.

Add a little extra olive oil if it still seems dry.

Set aside the filling until ready to use.

Preheat oven to 350°F.

In a food processor, pulse the garlic until well chopped.

Add the pinto beans, vegetable broth, olive oil and soy sauce and puree until mostly smooth.

In a large mixing bowl, mix together the vital wheat gluten, nutritional yeast, fennel seed, sweet paprika, dried thyme, dried sage, and fresh black pepper.

Make a well in the center and add the bean mixture.

Stir with a wooden spoon until the mixture starts coming together to form a ball of dough.

Knead until everything is well incorporated.

Place two pieces of tin foil (about 18 inches long) horizontally in front of you, overlapping the sheet further from you over the closer sheet by about 6 inches.

On a separate surface, flatten the seitan into a roughly 12 x 10 rectangle using your hands or a rolling pin.

Repair any holes by pinching dough from the ends.

Place the filling in the lower 1/3 of the seitan rectangle, leaving about 2 inches of space at both ends.

Form the filling into a nice, tight bundle.

Roll the bottom part of the seitan up and over the filling.

Keep rolling until it's in a log shape.

Pinch together the seam and sides to seal.

Place the roll in the center of the tinfoil and roll up like a tootsie roll, making sure the ends are tightly wrapped.

Transfer to a baking sheet and bake for an hour, rotating every 20 minutes for even cooking.

Test the roast by poking the roll with tongs; it should feel very firm.

If it doesn't, then bake further.

Remove from oven and let cool.

Unwrap, slice and serve.