Heat your oven to 190°C/Fan 170°C/Gas 5. Tip the buckwheat into a small pan. Pour in 400ml boiling water and add a pinch of salt. Cover, bring up to the boil and then turn the heat down and simmer for15 mins till the buckwheat is very tender.
While the buckwheat simmers, coarsely grate the courgette. Pop it in a sieve and add a pinch of salt. Stir through the courgette and then give it a couple of good squeezes to get as much water out as possible. Put to one side in the sieve, set over a bowl or sink to drain.
Drain and rinse the butter beans. Tip them into a food processor (no food processor? No problem, see our tip below).
Peel and grate or crush the garlic and add it to the food processor. Add 1 tsp of ground cumin and 2 tbsp of flour. Give the courgette another couple of squeezes to get out any remaining water and add the courgette to the processor. The buckwheat should be tender by now, so drain off any water, shake dry and add to the processor. Pulse a few times to make a chunky mix. Taste and add a pinch of salt or pepper if you think it needs it.
Line a baking tray with baking paper. Scoop 1 heaped tbsp of the butter bean mix out of the processor and pat into rough rounds with your fingers. Drop on the baking tray. Repeat, using up all the mix, and making roughly 8 falafels. Slide into the oven and bake for 20 mins till browned and a crust has formed all over the falafels.
While the falafels bake, trim, peel and coarsely grate the carrot and scoop it into a bowl. Peel and thinly slice the onion. Add it to the carrot. Trim the dry tips off the fennel and pluck off the fronds. Finely slice the fennel and add it to the bowl.
Roughly chop the parsley leaves and fennel fronds and add most of them to the bowl. Whisk the juice of half the lemon with ½ tbsp olive oil and some salt and pepper. Add to the bowl and toss to mix.
Squeeze the remaining lemon half into a small bowl. Add the tahini and 3 tbsp cold water. Stir to make a smooth sauce.
The falafels should be baked by now. Divide the slaw between 2 plates. Pop the falafels alongside it and drizzle over the tahini sauce. Garnish with the remaining chopped herbs and serve.