First, marinate the seitan: Toss all the marinade ingredients, except the seitan, into a small food processor and puree until (relatively) smooth.
Place the seitan in the marinade. Let marinate for about an hour, turning a couple of times to keep everything evenly coated.
Meanwhile, prepare the broth: Heat a stockpot over medium heat. Dry toast the coriander seeds for about 3 minutes, until they’re fragrant and a few shades darker. Add the peanut oil, onion, garlic, and ginger and sauté for about 15 minutes. Add the lemongrass, salt, broth, and 6 cups of water. Cover and bring to a boil. Once boiling, lower to a simmer and cook for about 30 more minutes, or until everything else is ready.
While the broth is simmering, prepare your noodles according to the package directions. Once they are ready, drain and rinse under cold water and set aside. It’s okay if they’re at room temp.
Then prepare the mock duck: Heat a large pan (preferably cast iron) over medium heat. Drizzle a little peanut oil in the pan. Sauté the mock duck for about 10 minutes, until nicely browned. Oh, and if you like things spicy, add a big pinch of red pepper flakes while sautéing.
Back to the broth. After it has simmered for 30 minutes or after all other components are ready, strain the broth through a fine-mesh strainer (remember to have a large bowl underneath, obviously), then return to the pot to keep warm. Add the lime juice.
To assemble the bowls, place one quarter of the noodles in each of four large bowls. Pour in the broth. Add sriracha to taste. Tuck the veggies and fresh herbs all over. Top with the mock duck and garnish with lime wedges. Serve with a fork or chopsticks and a large spoon.