Put the chopped onion, kale, 1/2 cup of cooked black beans (save the other 1/2 cup for later), and the flax egg in a food processor and process until relatively smooth. Pour the mixture into a bowl and add the remaining black beans, rice, sunflower seeds, oats, nutritional yeast, salt, and spices. Mix thoroughly.
Now grind the two slices of bread in the food processor until fine, and mix in as well. Form mixture into 8 patties. I found that these work great in the oven and the skillet.
For the skillet: set on medium heat, and once the pan is hot, spray lightly with olive oil. Cook burgers for a few minutes on each side or until lightly browned (which takes a few minutes – depending on your pan's heat).
For the oven: Pre-heat to 375 degrees Fahrenheit and bake on a well-oiled baking sheet for 10 minutes on each side, or until lightly browned. If you have a sporadically hot oven, check them at 7 minutes, and you may need to flip them early.