Pour 3 tablespoons (boiling) hot water over the flax seeds in a glass and set aside. (You can do this a little earlier so that the flax seeds swell longer.)
Drain and mash the peas and black beans. (I don't pound the mass very finely. I like it when you can still see what's inside the finished product.)
Peel and dice the onion and add to the pea and bean mash. Then add the swollen flax seeds and spices and mix everything together.
Then the breadcrumbs are worked into the mass. The amount of breadcrumbs needed can vary depending on the humidity of the peas and beans. It is therefore advisable to only take about 60g breadcrumbs at first and then add the rest as required. Meatballs formed from the mass should be dimensionally stable, but not crumble.
The mixture is sufficient for approx. 16 meatballs. I fry them on both sides in frying oil over medium heat.