Add all the marinade ingredients to a bowl and stir until well combined. Cover and refrigerate for at least 15-30 minutes, ideally for 2 hours or even overnight.
Drain the seitan, but don’t discard the marinade. Cook the seitan in a skillet over medium-high heat for 5-10 minutes or until golden brown. Set aside.
Add the veggies (onion and peppers), salt and marinade to the skillet. Stir and cook over medium-high heat for 5-10 minutes or until golden brown. Add some oil if needed.
Add the cooked seitan to the skillet, stir and cook for 1-2 more minutes. Enjoy immediately just by itself or with some tortillas and your favorite toppings (like avocado, tomato or lettuce), sauces (guacamole, sour cream, salsa) or sides (rice, beans).
Keep leftovers in a sealed container in the fridge for 5-7 days or in the freezer for up to 3-6 months.
Feel free to use homemade or store-bought seitan.
If you can’t eat gluten, use any other meat alternative like tofu, tempeh, mushrooms or even legumes instead of the seitan.
Use any veggies or oil you have on hand. If you’re oil-free, use some water or vegetable stock instead.
If you don’t like your food spicy, just omit the red pepper flakes. You can also add any other ingredient to make your fajitas spicy like sriracha, jalapeños, cayenne powder, etc.