It's better to prepare the steaks a day before frying them.
For the vegan seitan steaks:
1 1/2 cups vital wheat gluten
1 cup cooked lentils (you can use canned lentils)
6 tablespoons water
2 tablespoons nutritional yeast
2 tablespoons tomato paste
2 tablespoons soy sauce
1 teaspoon garlic powder
1 teaspoon chili powder
1/2 teaspoon liquid smoke
1/4 teaspoon black pepper
For the vegan seitan steak marinade:
1/4 cup water
2 tablespoons olive oil
2 tablespoons soy sauce
1 tablespoon maple syrup or agave
To make the vegan seitan steaks:
Add all of the vegan seitan steak ingredients to a food processor and pulse to combine, stopping to scrape down the sides as needed until everything is well mixed. Alternatively, if you do not have a food processor you can first mash the cooked lentils with a fork or potato masher, then add everything together in a large bowl and mix well.
Turn the mixture out onto a clean work surface and begin to knead it together. It may be a bit crumbly at first, but keep kneading it for a few minutes until it comes together into a tight ball. Cut the ball into 4 sections, then use a rolling pin to roll out each section into 1/2" thick steaks. The dough will be very tough and stretchy, but just keep working at it until you get your desired steak shapes.
Add several inches of water to a large pot with a steamer basket and bring to a boil. Put the steaks in the steamer basket and cover with a lid. It's ok if they are overlapping a bit. Steam for 25 minutes, flipping the steaks halfway through so they steam evenly. They will double in size.
In a large ziplock bag or air-tight container, mix together all of the marinade ingredients. The oil won't really combine, but that's fine. Remove the steaks from the steamer and coat in the marinade. Let marinate for a minimum of 30 minutes before cooking, or for as long as several days when kept in the fridge.
To serve the vegan seitan steaks:
When you are ready to enjoy the vegan steaks, heat a frying pan, grill pan, or barbecue. When hot, fry or grill the steaks a couple of minutes on each side until grill marks form. Brush the steaks with leftover marinade while cooking and also right before serving to keep them juicy.
Note: it's important to knead the dough well or it will be spongy.
I recommend you watch these videos below before making seitan.