Put the onion, garlic and fresh herbs into a small food processor and blitz for a few seconds. Add the beans and spices, then process again for a few seconds - don’t purée it, the mixture should be coarse! Rest for 10 minutes.
Meanwhile cut the courgette in half. Grate half of it, add some salt and rest for 10 minutes, then squeeze out the liquid. Mix the courgette with the beans, season with salt and pepper, then form 3 large or 4 small patties.
Heat a griddle pan, BBQ or grill. Spray the patties with oil then cook them for 3-5 minutes on both sides.
Meanwhile cut the buns in half and lightly toast the cut sides. Slice the remaining half of the courgette, spray these with oil and grill them too until charred.
Assemble the burger with your chosen condiments, the bean patties and courgette slices. Alternatively, serve it with chips or sweet potato wedges. For a low-carb version, serve the patties with more grilled courgette slices and a green salad.