Hash is comfort food from leftovers. You fry some onions, throw in cold meat and potatoes and perhaps some gravy, let a crust develop, and turn the mass as best you can to brown the other side. The problem, I find, is that bits of the mixture stick to the pan. I prefer to form the potato (mashed) and meat into cakes; but then the problem is that the cakes fall to bits. Binding them with flour produces a glutenous texture. As I have written before, the best technique -- though not an infallible one -- is to fry the cakes quickly and transfer them to a baking sheet in the oven before they have a chance to disintegrate.
My potatoes were not leftovers. Cooking for two of us, I cut up and simmered four medium ones until tender. I drained them and let them cool. (Their texture tightens: that is not what you want for fluffy mash, but it produces the more adherent mass you need here.) I had a small bag of sprouts -- about 150 to 200 g, I should guess. I steamed them for seven minutes, until they gave a little but retained some crunch. I chopped them roughly. I chopped a large handful of parsley. I chopped about two large handfuls of cold chicken. I mashed the potato, and mixed it with the other ingredients as well as salt and pepper. I formed the mixture into six cakes, which I fried in hot groundnut oil for a couple of minutes on each side, before giving them 10 minutes in the oven at gas mark 6/200 C.