In a pan, cover the potatoes with water and bring to the boil. Simmer for 8-10 minutes. Drain well, mash and set aside.
Meanwhile, put the quinoa in a pan with plenty of water, bring to the boil and cook for 7 minutes. Drain, rinse under cold water and set aside.
Tip the dried mushrooms into a bowl, cover with boiling water and leave for 5 minutes. Then strain and chop.
Heat half the oil in a large frying pan, add the fennel seeds and cook for 2 minutes. Tip in all the mushrooms, add half the lemon juice and fry for 8-10 minutes until softened and all the moisture has evaporated.
In a bowl, mix the mash, quinoa and mushroom mixture with half the chilli, the parsley and lemon zest. Season and stand for at least 30 minutes to firm up. Form into 8 patties (you can do this up to a day ahead, just chill until needed).
When ready to serve, heat the oil in a large frying pan and cook the patties for 3-5 minutes each side until golden brown and hot all the way through.
For the mayo, mix the mayonnaise with the chilli sauce, the remaining chilli and the rest of the lemon
juice. Serve the burgers in bread rolls with some rocket, chilli mayo and lemon wedges. Non-veggies might like to add some crispy pancetta or streaky bacon, too.