Fill a small to medium saucepan with water to halfway and add the vinegar. Bring to the boil and reduce to a simmer.
Place a mesh strainer (the mesh needs to be quite tightly woven, like a tea strainer) over small bowl or cup. Break the egg into the strainer and allow to sit while the thinner part of the egg white drains away into the bowl, about 1/2 a minute. You will be left with just the thickest part of the white and yolk (be careful not to break the yolk).
Gently tip the egg out of the strainer into the simmering water. No need to touch the egg or do anything, leave it to poach for about 2 minutes until the yolks are still springy to the touch and fluid. Remove with a slotted spoon, drain and serve.
Serve on toasted sourdough topped with mashed avocado, salt, pepper, feta and a sprinkling of Dukkah.