Preheat oven to 350 F. In a food processor, pulse the garlic until well chopped. Add the beans, broth, olive oil and soy sauce and puree until mostly smooth (a few pieces of bean are okay, but they should be no bigger than a pea.)
In a large mixing bowl, mix together the wheat gluten, nutritional yeast, herbs and spices. 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.
Now we’re going to roll out the seitan and form the roast. Place two pieces of tin foil (about 18 inches long) horizontally in front of you. The sheet further from you should overlap the closer sheet by about 6 inches. This way you have enough foil to wrap around the whole roast.
On a separate surface, use your hands or a rolling pin to flatten the seitan into a roughly 12 x 10 rectangle. If any pieces rip, don’t worry about it, just use a pinch of dough from the ends to repair any holes.
Place the filling in the lower 1/3 of the seitan rectangle, leaving about 2 inches of space at both ends. Make sure the filling is compact, use your hands to form it into a nice, tight bundle.
Now roll! Roll the bottom part of the seitan up and over the filling. Keep rolling until in it’s in a log shape. Now pinch together the seam and pinch together the sides to seal. It doesn’t have to be perfect, it will snap into shape when baking.
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*. Rotate the roll every 20 minutes for even cooking.
* I may update the time in this recipe because I’ve gotten a few comments that said it took up to 90 minutes to cook completely! So for now I would say just do a test my poking the roll with tongs. It should feel very very firm. If it doesn’t, then bake further.
Remove from oven and let cool. Unwrap, slice and serve! (See recipe notes for keeping moist and reheating.)