Mash the beans with a fork, add the sweet potatoes and all the other ingredients up to and including the linseed, season. Knead by hand to form a compact mass. Divide the mixture into 4 portions, shape into 4 burgers, flatten a little.
Cut half of the mini cucumbers lengthwise into thin slices, set aside. Finely chop the remainder of the cucumbers, mix with the sour single cream and oil, season with salt.
Brush the burgers with oil, cover and grill over/on a medium heat (approx. 220 °C for approx. 10 mins. on each side. Grill the halved burger buns alongside for approx. 1 min. Spread the cucumber sauce over the bottom half of each bun, add the burger, top with the cucumber slices, micro greens and a little more sauce, cover with the top half of the bun.