Cut potatoes into 5 mm (1/4) in slices, then into 5 mm (1/4 in) dice. Rinse with cold water. Drain well and dry on absorbent kitchen paper.
Heat oil in a heavy frying pan. Add potato and onion, cover and cook over a medium heat, shaking pan frequently until tender, about 15 minutes. Add the ham, mix well and heat for 5 minutes. With the back of a large spoon, make four indentations, in the mixture. Break eggs one at a time onto a saucer then carefully slide into each indentation. Cover, and cook until eggs are set, about 5 minutes.. Peel, stone and slice the avocado. Serve the eggs and potatoes garnished with avocado slices and coriander.