In a large bowl, roughly mush the beans with a fork or potato masher, but not too much, keeping a few chunks in the mixture for added texture.
Add in the lime zest and juice, cumin, garlic powder, flax seed, salt, pepper and chilli flakes. Mix well to combine.
Taste the mixture and adjust as appropriate. Pop in the refrigerator for around 15 minutes to firm up.
Take the mixture out of the refrigerator and form 4 balls with the mixture. Press each one firmly to shape into a burger patty.
Cook them over a medium low heat on the grill, turning occasionally, for about 7 minutes each side. Optionally, use a grill pan to help the patties keep their shape better. Brush with BBQ sauce for extra flavour!
Serve with a soft burger bun and fries, or on its own!
