Preheat oven to 400 degrees F (204 C) and cut sweet potatoes in half. Rub with olive oil and place face down on a foil-lined baking sheet. Bake sweet potatoes until soft and tender to the touch - about 30 minutes - set aside. Reduce oven heat to 375 degrees F (190 C).
While potatoes are baking, cook rice or quinoa (see notes for instructions).
Add black beans to a mixing bowl and mash half of them for texture. Then add sweet potato and lightly mash, then 1 cup rice (amount as original recipe is written // if altering batch size, start with lesser end of range), green onion, nut meal and spices. Mix to combine. Taste and adjust seasonings as needed. Add more rice or nut meal if the mixture feels too wet. It should be very moist but moldable.
Lightly grease a baking sheet and line a 1/4 cup measuring cup with plastic wrap.
Fill the lined measuring cup with sweet potato mixture. Scrape down to pack, then lift out and transfer to the baking sheet and gently press down to mash. The thinner you press them, the faster they’ll cook, but no need to go too far. Just a gentle press will do.
Bake burgers for a total 30-45 minutes, carefully flipping 20 minutes in to ensure even cooking. The longer you bake them the firmer and drier they will get - up to preference. I went for around the 35 minute mark.
Serve on slider buns (double stack for more bulk) or atop a salad with sliced avocado, red onion, greens, and ketchup or salsa.
Store leftovers covered in the fridge for up to a few days. Freeze for longer term storage.
Freezing instructions: par-bake for ~20 minutes (instead of 30-45 minutes), let cool, and then carefully layer between pieces of parchment paper and enclose in a freezer bag or container with a secure lid. Reheat them from frozen at 375 degrees F (190 C) for about 20-30 minutes or until desired firmness.
*To cook rice: bring 2 cups water to a boil. Then add 1 cup very well-rinsed rice, reduce heat to simmer, cover, and cook for about 30 minutes or until fluffy and tender. You will have leftovers. *For quinoa: rinse 1 cup quinoa and add to a saucepan over medium heat. Sauté in a bit of olive oil for 1-2 minutes, then add 2 cups water and bring to a boil. Reduce heat to simmer, cover and continue cooking for about 15 minutes or until tender and fluffy and the water is absorbed. *For veggie burgers that hold up well on the grill, try our Easy Grillable Veggie Burgers or Smoky BBQ Black Bean Burgers. *Inspired by the Black Bean Burger at Beer Kitchen *Nutrition information is a rough estimate calculated with lesser amount of rice, with walnut meal, and without optional ingredients.