Combine vital wheat gluten, bread flour, onion and garlic powder in an 11-cup (minimum) food processor fit with an ‘S’ blade. Pulse to combine.
Add remaining Seitan Roast ingredients to a high-speed blender and blend until smooth.
Add blender ingredients to dry ingredients; pulse to combine, then allow the machine to process dough until it begins laboring to continue turning it; this is the best indication that the gluten strands have properly developed.
Remove dough from food processor, form into a tight ball, place in a mixing bowl, cover with a tea towel and allow it to rest for 15 minutes.
Divide dough in quarters and shape each piece into a rough cylinder.
Roll up tightly with heavy duty aluminum foil, folding in the ends to create a package which will hold the steam in during cooking. Double-wrap each piece and place on a steam rack in an 8-quart pressure cooker (InstantPot) with 2 cups of water in bottom of cooker.
Steam on high pressure 90 minutes and allow to naturally release 20-30 minutes beforeremoving from cooker. When cool enough to touch, remove foil and gently pierce roasts with a fork 3-4 times on each side.
Add to Simmering Broth and allow to simmer uncovered 45 minutes, turning occasionally.
Transfer roasts to plastic zip bag or storage container, and cool completely in refrigerator 4 hours or overnight. Slice roasts on the bias to create medallions for pan glazing.