1Bring stock to boil. Add quinoa and sweet potato; cook for about 10 mins. Add the kidney beans for the last 5 mins. When the sweet potato is tender and the quinoa is cooked, drain well and cool.
2Put all remaining ingredients (except olive oil) in a bowl. Add the cooled bean and quinoa mixture. Squash the mixture with a rolling pin, crushing the beans and potato as you go. Season with salt and ground pepper.
3With wet hands, form 8 medium-sized or about 15 small rounds from the mixture. Place on a plate and chill in the fridge for at least 40 mins.
4Heat half the oil in a frying pan. Cook mixture rounds in batches over medium-low fire for about 3 mins each side. Repeat with the next batch.
5Serve with avocado, tomato salad and lime wedges.
Photo: Bauer/Jonathan Gregson