1Heat the oil in a saucepan and gently cook the onions until starting to brown, stirring regularly.
2Add the mince and cook for 10 minutes, breaking up any clumps as the mince softens.
3Add the carrots, celery and canned lentils into the pan and cook for another 5 minutes, stirring regularly.
4Add the garlic, herbs and chilli flakes and stir for a minute. Add the vegetable stock followed by the canned tomatoes.
5Bring to a gentle simmer, cook and cover for 15 minutes, stirring occasionally and adding a little water if too much water evaporates and the ingredients begin to stick to the pan.
6Meanwhile in another pot boil spaghetti according to pack instructions.
7Once the sauce is cooked, sprinkle black pepper into the sauce.