1) Chop and saute the red onions in the olive oil until golden. 2) In another pan saute the sausages until nicely browned. 3) Once the onions are golden add the tinned tomatoes, thyme, salt and pepper, celery and carrots and simmer for 20 minutes. 4) Add the lentils to the casserole and simmer for a further 20 minutes until the lentils are tender. 5) chop up the cooked sausages and add to the casserole and simmer for a further 10 minutes and serve sprinkled with parsley or leave overnight and reheat for maximum flavour.