Place the vital wheat gluten in a large bowl.

Put the water, oil, tamari, tomato paste, vinegar, smoked paprika, sugar, fennel seeds, red pepper flakes, and ground mustard in a blender and process until the fennel seeds are coarsely ground.

Pour into the vital wheat gluten, add the garlic, and combine thoroughly with a sturdy silicone spatula to form a dough. Knead the dough in the bowl until it exhibits some elasticity, about 1 minute. Divide the dough in half.

Lay a 12-inch-long sheet of heavy-duty aluminum foil on a work surface. Shape one portion of the dough into a slender log about 6 inches long and place it near the edge of the foil. Lift the edge of the foil over the dough and begin rolling into a tight cylinder. Twist the ends tightly to seal. Bend the ends in half to lock them tight. Wrap in a second sheet of foil in the same manner. Repeat the shaping and double-wrapping technique with the second portion of dough. If you will be oven baking the dough (rather than pressure cooking it), wrap each package in a third sheet of foil for reinforcement.

To pressure cook, put 3 cups of water in the cooker and put the trivet in place. Add the packages, seal the lid, close the steam valve, and cook on high for 1 hour. Turn the unit off and let the pressure release naturally for 30 minutes.

To oven bake (instead of pressure cook), preheat the oven to 325 degrees F (170 degrees C). Put the packages directly on the middle oven rack and bake for 1 hour and 15 minutes.

Remove the packages and let cool. Then refrigerate the packages for 8 hours to optimize the texture and make thin slicing easier. The pepperoni is ready to eat or use in recipes; it does not require any additional finishing. Slice thick or thin and use as needed.