Heat oil in a large skillet over medium heat and sauté the onions for 5 minutes, or until they are soft and translucent.

Add the seitan, cumin, paprika, garlic powder, onion powder, and lime juice to the skillet and stir to combine.

Sauté until the seitan is golden brown and warmed through, about ten minutes.

Fill taco shells with seitan mixture, top with desired accompaniments and serve.