Brown the sausages in which ever way you would choose. My preference would be under the grill.
Brown the lardons in a large casserole or saute pan (big enough to hold the whole dish). There's no need to add oil - the lardons will provide their own.
Add the onions, carrot and garlic to the lardons and cook for a further 3-4 minutes until the onions are softened.
Add the sausages, rosemary, lentils, stock, vinegar and chopped tomatoes to the pan and season with salt and pepper.
Mix throughly and gently bring to the boil and simmer rapidly for 5 minutes. Now lower the heat, cover and simmer for 45 minutes. Check in every so often to be sure that you don't need to add any more liquid. At this stage, the dish can be chilled to reheat later or frozen.
Check the seasoning, scatter over the parsley and serve from the pan.
This dish reheats beautifully, but you will always need to add a splash or two of water to loosen it up.