Heat half the oil in a large frying pan on high. Saute onion for 4-5 mins, until tender. Stir in cumin and cook for 1 min, stirring, until fragrant. Set aside to cool.
Place lentils in a food processor. Process until almost smooth and transfer to a bowl. Stir through carrot, egg and breadcrumbs. Season to taste.
Shape mixture into 4 evenly sized patties. Cover and chill for 20 mins, until firm.
Heat remaining oil in same pan on medium. Fry patties, for 2-3 mins each side, until golden. Drain on paper towel.
Spread one half of each piece of bread with hummus. Top with beetroot, lettuce, patty and reserved onion. Top with remaining bread.
