Place lentils in a medium saucepan and cover with stock, bring to the boil, cover and simmer for 10-15 minutes or until tender, drain if there is any excess liquid. Allow to cool.
Heat half the oil in a large frying pan over medium heat and cook onions until golden and caramelised. Set aside.
Combine cooled lentils with mince, garlic, egg, breadcrumbs and a little freshly cracked pepper. Form into 4 rissoles and refrigerate until ready to cook.
Heat remaining oil in same pan onions were cooked in and cook rissoles over medium heat for 5 minutes each side or until cooked through.
Toast rolls and assemble with rissoles, onions, tomato, beetroot, lettuce and sauce.
