Place lentils in a pot with enough water and bring to the boil. Simmer for 30-40 minutes or until soft. Drain well and cool.
Mash lentils and butter beans with a fork or potato masher and mix with the remaining ingredients, except the oil.
Heat some of the oil in a frying pan. Spoon about ¼ cup of the mixture into the pan per patty. Fry patties over a medium heat. When the top begins to set, turn over and fry until golden brown. Repeat with the rest of the oil and mixture.
Serve on a wholewheat roll as a hamburger with lettuce, tomato and cucumber.