Place the vital wheat gluten flour in the bowl of your stand mixer. Set aside.
Place all of the remaining ingredients in a food processor or blender and blend until smooth.
Pour the wet ingredients into the bowl with the flour and knead with the dough hook for about 10 minutes. The dough should form a smooth and relatively stiff ball.
Divide the ball of dough into two equal pieces and wrap each piece tightly with some parchment paper, foil or cheesecloth.
Place the steaming basket or trivet in your Instant Pot, and add enough water to come just up to the trivet. Place the wrapped seitan in the Instant Pot and cook on high for 1 hour.If you don't have an Instant Pot, simply place some water in a stock pot, place a steamer basket on the bottom, cover, and steam the wrapped seitan for 1½ hours.
Allow the pressure to release for 10 minutes, then open the vent to release remaining pressure.
Carefully remove the seitan and let it cool. The more the seitan cools the firmer it will get.
For the wrap:
You will only need one of the seitan pieces for these wraps. You can freeze the remaining piece, either whole or sliced.
Thinly slice the seitan gyro.
Add one tablespoon of olive oil in a pan and cook the sliced gyro for about 1 minute per side. It does not need to cook for very long or it will get too crunchy.Sprinkle with some thyme and oregano, and salt & pepper to taste.Drizzle with a squeeze of fresh lemon juice.
Place some greens, tomato slices, onion, and gyro slices in each of the pitas. Top with some tzatziki sauce and serve.