Preheat oven to 400°F.

In a small bowl, combine the spice mixture: cumin, chili powder, dried thyme, dried sage, celery seed, white pepper, black pepper, cayenne, and 1 teaspoon salt. Mix well and set aside.

Drain the whole canned tomatoes, reserving the liquid. Coarsely chop the tomatoes.

Place the seitan in a food processor and pulse about 12 times until shredded to create a meat-like texture.

In a Dutch oven with a lid, combine the reserved tomato liquid with vegetable broth and bring to a boil over medium-high heat.

Add the uncooked brown rice and 1/4 teaspoon salt to the liquid. Return to a boil, then cover, reduce heat, and simmer for 20 minutes.

Meanwhile, heat olive oil in a separate pan over medium heat. Add onion and cook until slightly softened, about 3 minutes.

Add garlic, red bell pepper, and celery to the onions. Stir in the prepared spice mixture and cook for 2 minutes until fragrant.

Add the chopped tomatoes to the vegetable mixture, followed by the shredded seitan. Cook for about 3 minutes, stirring occasionally.

Transfer the vegetable-seitan mixture to the Dutch oven with the partially cooked rice. Stir to combine thoroughly.

Cover the Dutch oven and bake in the preheated oven for 30-45 minutes, until all liquid is absorbed and rice is tender.

Remove from oven and let rest, covered, for 5 minutes.

Stir well before serving and garnish with fresh flat-leaf parsley.