2tablespoonsoil(optional) It's your choice what kind, I use olive. If you don't use any use a good non-stick pan to cook them in
Add beans to a large bowl and mash roughly with a potato masher (but not too much).
Add all of the other ingredients and mix well (I find clean hands are the best tool for this), making sure everything is well combined. Taste the mixture to check seasoning and add more if necessary.
Refrigerate for about 15 minutes. This helps it firm up a little and makes it easier to shape the burgers.
The mixture will feel very sticky but should come together well. Shape into 4 balls, pressing them together really really firmly then using the palm of your hand press down on the top of each one to make it a burger shape. If they crack a bit just press them gently back together. If you struggle to shape them because you feel the mixture is too sticky then add a few more tablespoons of flax or some bread crumbs and leave for a few minutes to let it absorb some moisture before attempting to shape again.
Once hot add the burgers making sure there is plenty of space around each one to enable you to flip them later. If you can't fit them all in, have your oven on low (300 degrees F) and once the first ones are done keep them warm in there until the rest are ready.
Fry them for about 5 minutes each side or until a nice golden crust forms.
To oven bake
Put the burgers on a lined tray and bake them in the oven on 375°F until heated through and a bit crusty on the outside (about 30 minutes).
nutritional info calculated without the optional oil