As always, I changed something. I used a lot more beans that the recipe requires but didn't really change the rest. Perhaps I used a bit more carrot, I'm not sure. Also, instead of mashing everything down I used Thermione, which gave a smoother texture although I was careful not to completely puree it. A stick blender or other type of zizzer would do just as well. Finally, I left the mixture overnight in the fridge and I think that helped the flavours to develop.
The outcome was seven really decent sized burgers which I open froze before bagging. One would be fine in a bap with the trimmings or two if eaten as part of a main meal without bap, etc.
I won't reproduce the recipe here but here's the link and a photo borrowed from Jack's site. Well worth making!