Prepare the ingredients. To make breadcrumbs, either grate the slice of bread on a grater, or pop in a food processor.
Add the first five ingredients to a bowl and mix well. Stir in the onions then mash in the meat with a fork until all ingredients are combined.
Form 4 - 6 balls, then flatten into burgers.
If cooking in a frying pan, add the oil and once hot, placing the burgers in the pan, starting with the outside and work inwards. You may need to cook them in batches if using a small pan.
Turn the heat to medium, and cook for 5 mins. Turn each burger over, cover with a lid or foil, and cook for another 5 mins. If your burgers are quite chunky, they may need a bit longer. The inside of the burgers should be cooked thoroughly with no pink juices.
To cook in the oven, pre heat to 220c, add the burgers to an oiled tray and bake for 10 - 15 mins, depending on their size.