Dredge the slices of seitan in flour.
Warm a tablespoon of olive oil in a large skillet over medium heat.
Combine aquafaba with salt, pepper and garlic powder in a deep dish or bowl. Dip each flour-coated piece of aquafaba mixture and then cover both sides with breadcrumbs.
Cook breaded slices of seitan in warmed skillet about 2 - 3 minutes per side, until golden brown and crispy.
Set aside cooked slices and keep warm.
Add remaining olive oil to skillet, stir in sliced red onion, and cook for 2 minutes.
Add minced garlic and cook an additional 3 minutes.
Sprinkle 1 tablespoon flour into skillet and cook until golden, about 3 minutes, stirring constantly.
Slowly stir in the vegetable stock and cook until thickened, about 5 minutes.
Add lemon juice and capers to skillet. Season to taste with additional salt and pepper. Stir to combine.
Spoon sauce over cooked seitan. Serve and enjoy!