Puree the tempeh in a food processor until very fine (Alternatively you can do this with a fork but it will take a lot longer and may not get to the desired consistency.) Add the tempeh, vital wheat gluten and onion powder to the bowl and mix thoroughly. Now add in your liquids. Mix together and knead the dough for 3-4 minutes. Let it rest for 5 minutes. Now separate into 4 portions and stretch each portion out into a thin cutlet shape.