For the burgers:

1. Preheat the oven to 350 degrees F. Line baking sheet with parchment paper.
2. Arrange mushrooms in an even layer on baking sheet, drizzle with 1 tablespoon olive oil and season with salt and pepper to taste. Roast mushrooms until tender and shrunk in size, about 12-15 minutes. Let cool.
3. Pour black beans onto baking sheet and roast until dry and split open, about 7-10 minutes. Let cool.
4. Heat 1 tablespoon olive oil in medium nonstick pan over medium heat. Add onions and cook until translucent, about 5-7 minutes. Add garlic and cook for another 60 seconds or until fragrant. Let cool.
5. In a food processor, pulse walnuts and quinoa flakes until finely chopped. Add mushrooms, beans, onion and garlic, and brown rice and pulse until combined and finely chopped.
6. In a large bowl, whisk together egg yolk, miso, Greek yogurt, chipotle powder, chili powder and cumin. Add burger mixture to bowl and mix until combined. Salt and pepper, to taste.
7. Form mixture into 6-8 burger patties.
8. Heat 1 tablespoon olive oil over medium heat in nonstick or cast iron skillet. Cook patties until browned, about 5 minutes on each side. If using cheese, place slice of cheese over top of burger, cover and let cheese melt for about 1 minute.
9. Serve on buns with special sauce and desired toppings.

For the special sauce:

1. In a smal bowl, whisk together, yogurt, ketchup, relish, mustard and sriracha. Spread on hamburger buns as desired.