In a small bowl, mix together the ground flax & water to make flax eggs. Set aside about 10 minutes. It will thicken up and become gel-like.
In a large bowl, mash the drained beans with a fork or potato masher. Add the rice, walnuts, oats, arrowroot powder, prepared flax eggs, tomato paste, worcestershire sauce, tamari & liquid smoke. Combine really well & set aside.
In a large pan, heat the oil over medium heat. Sprinkle with salt. Sauté onion for 3-4 minutes, until translucent. Add garlic and sauté for 1-2 minutes.
Add the mushrooms turn the heat up to medium-high. Sauté until they release their liquid. Cook liquid completely off or there will be too much moisture. About 6-7 minutes. Now turn the heat back to medium and add the paprika, cumin & oregano. Sauté for 1-2 minutes. Remove from heat.
Transfer the cooked mixture into the large bowl of previously mixed ingredients. Combine well, using hands if necessary. Add cracked pepper and taste to see if it needs any more seasoning. Place mixture uncovered in the freezer for 25 minutes or the fridge for 45 minutes or more. This helps firm it up and meld the flavors a bit.
Form the mixture into individual patties, keeping the size of the burger buns in mind. Create a ball with the mixture and place on a large piece of parchment paper. Now flatten evenly with your hands to create a 1/2" disc. Smooth out sides and any cracks with your hands. Repeat until the mixture is gone. * I used 1/2 cup of mixture to form 1/2" thick patties to fit a 3.5" burger bun.