Put the beans in fresh clean water and cover them with at least 2" (5 cm) of water. Bring to a boil and remove any foam that forms. Reduce heat to a bare simmer and cook until tender. The time will vary depending on your own beans, but you are looking at approximately 45 minutes. Remove lid off to cool and set aside. Drain if there is any water left. If you're using already cooked black beans, use 1 1/2 cups,
While the beans are cooking, prepare the brown rice. Using a large pot, cover the brown rice with 1 1/4 cups (300 ml) of water. Bring it to a boil. Then reduce heat to low and simmer, covered, until tender (for about 40-50 minutes). Let stand 5 minutes, then fluff with a fork.
In the meantime, grind the toasted walnuts in the food processor until they resemble a loose meal (breadcrumbs).
To grill the burgers, preheat your grill over medium heat. Cook for about 5 minutes, then flip gently. Cook for 4-5 minutes on the other side. To bake the burgers, arrange the burgers on a baking sheet coated with olive oil. Bake at 375°F (190°C) for 30-40 minutes, flipping halfway through. To fry the burgers, heat a little bit of olive oil in a frying pan and cook the burger on one side until golden, about 6 minutes. Then flip and cook on the opposite side.
Store leftover veggie burgers covered in the refrigerator for 3-4 days.
For long term storage, cook burgers as instructed on the grill or in the oven. Then set on a baking sheet or plate and freeze. Once completely frozen, place the burgers into an airtight container and store for up to 3 months. Reheat in a 325°F (165°C) oven on a bare baking sheet until warmed through.
*Soak the beans in water for at least 8 hours (or overnight). To quick-soak beans, pour boiling hot water over the beans and soak for 1 hour uncovered. When the beans are done soaking, drain the water and rinse the beans thoroughly.
*3/4 cup dried black beans is equivalent to 1 (15 oz/398 ml) can or 1 1/2 cups (278 g) cooked (drained) beans.
**1/2 cup uncooked brown rice equals 1 cup (150 g) cooked rice.
***Prep time does not include soaking the beans (8 hours). Cook time includes cooking the beans, the rice, and grilling the burgers.