Soak and boil the lentils with the vegetable stock (follow package instructions).
Bring the oven to 160°C/325°F/gas mark 3.
For the burgers: bring a pot to medium heat and add the red onion, garlic, thyme, oregano, walnuts, dates, salt and water. Let this boil for three to four minutes, until the onions start to soften.
Take the pan off the stove, add the boiled lentils and the soy flour and mix it all together using a hand blender. The consistency should be firm, but not too dry. Adjust with more water or more flour if needed.
Place a cooking paper onto a baking tray. Shape burgers out of the lentil/walnut mix and place on the paper. Bake in the oven for 20 minutes.
In the meantime, make the relish: place the chopped onion, raisins, dates, sage leaves, salt and the water in a pot and bring to boil on low heat under a lid. Leave boiling until serving time. Stir occasionally and add a little more water if needed.
Then make the purée: boil the broccoli and the cauliflower together with the vegetable stock for about three minutes. Then remove all water, add the salt and the milk and blend into a purée.
Get the burgers from the oven and serve with the relish and the purée on the side.