In a large bowl, mix together vegan mayo, ketchup, and mustard.
To that bowl, add biscuit pieces, most of the Bacon Seitan and Ground Seitan (reserving a small amount for the topping), 1 cup vegan cheddar, and a handful each of the sauteed onion and chopped tomato. Mix gently.
Transfer mixture to a greased cast iron skillet and spread it out evenly.
Sprinkle on additional seitan, tomato, onion, and the remaining vegan cheese.
Cover with foil and bake for 30 minutes, or until the biscuit pieces are baked through.
Uncover and cook for an additional 5 minutes until bubbling, and the cheese is melted.
Remove from oven and garnish with chopped pickles and sesame seeds, if desired. Allow to cool slightly, and serve warm.