Dough: Add mushrooms to a food processor and blitz a few times, until finely broken down. Add tomato paste and spices, then blitz again to combine. Add wheat gluten, and blitz just until it comes together into a cohesive mixture. Do not over mix.
Shape: Portion dough into 8 balls, then flatten each as much as possible into a hamburger shaped patty (they will expand when cooking, so flatten them more than you would like them to be when finished).
Broth: Add all broth ingredients to a large pot and bring to a simmer. Gently lower the seitan burgers into the broth, ensuring the dough is covered by the broth (if not, transfer to a smaller pot). Partially cover and simmer for 30 minutes. When finished, remove patties from liquid.
Sear: Sear patties on a well greased pan or grill over high heat to slightly char the outside, then serve as you would a regular hamburger!
*For a more beefy flavor, use a vegetarian "beef" broth, such as Better than Bouillon No Beef Base