Preheat a large oven-to-table Dutch Oven or heavy pot over medium-heat. Saute the seitan in 2 T oil for 4-6 min, until lightly browned. Remove from the pot and set aside.
Add the remaining olive oil to the pot, then stir in the onion, celery, green pepper, and garlic. Saute for 12-14 minutes, until the vegetables are very soft and a tad mushy. Stir in the tomato paste and cook, stirring frequently, for another 4 minutes.
Stir in the cooking sherry to deglaze the vegetables, cook for 30 seconds, then add the rice. Stir the rice for about 4 minutes, then stir in the diced tomatoes, seitan, beans, bay leaf, all of the herbs, and the salt and pepper. Bring to a simmer, pour in the vegetable broth, and return to a simmer. Taste the broth and adjust the salt and pepper to taste.
If using a Dutch Oven, cover and place in oven for 30-35 minutes, until the rice is tender. If using a pot, transfer to a deep casserole dish, cover tightly with aluminum foil, and bake for 30-35 minutes. If using brown rice, increase the baking time to 40-45 minutes.
Remove from the oven, stir the jambalaya, then cover and allow to sit for about 10 minutes before serving.