Preheat oven to 350°F (175°C).
Blend wet ingredients: Add everything except the vital wheat gluten to a food processor. Blend until completely smooth.
Add vital wheat gluten: With the processor running, add the vital wheat gluten one spoonful at a time through the chute until a dough ball forms.
Knead in food processor: Run the food processor for 2–3 minutes to knead the dough ball, until it is smooth, soft and stretchy. The seitan dough should be able to be stretched thin without tearing (passes the windowpane test).
Shape the seitan: Form the dough into a ball, then divide into 4 equal pieces. Shape each into fillets about ¾–1 inch (2–2.5 cm) thick.
Prepare the dish: Oil a 9x13-inch (23x33 cm) glass or ceramic baking dish. Place the fillets inside and coat all sides with oil. Add 2 tablespoons of water to the pan, then cover tightly with foil.
Bake until cooked through.
