In a food processor, add in the chopped onions and the clove of garlic. Process until everything is minced finely.
Then, add in the oats, breadcrumbs, walnuts, flaxseed, salt, and spices. Process until the mixture forms a chunky meal.
Then add in the black beans and olive oil, plus 1 tbs of water. Process until the mixture is chunky and pliable (there should still be some chunks of black beans in the mixture - you don't want it to be totally smooth).
If the dough is too crumbly, add in the additional 1 tbs of water.
Let the dough rest for 10-15 minutes. DO NOT skip this step!!
Then, cut the dough into four even portions.
Bring a sauté pan to medium heat with a drizzle of a neutral vegetable oil.
While the pan is heating, shape the dough into burgers. (Use the photos here for a reference.)
Cook each burger in the pan with oil for about 4-5 minutes on each side.
Serve the burgers on your favorite bun with lettuce, tomatoes, and red onion. (Or any fillings you like!)
I have not tried grilling these burgers (I don't own a grill!) so I don't know if they'd work out using that cooking method. I think they'd hold together in a cast iron grill pan, but I wouldn't try them on a traditional barbecue grill.