Boil the lentils in the broth for about 10 minutes and then drain. However, collect some of the broth.
Heat the fat in the pan and sweat the onions and garlic clove in it. Fry the minced meat in it too.
Put the diced bell pepper with the lentils and tomato paste in the pan. Deglaze the whole thing with part of the collected stock and bring to the boil briefly. Season to taste with salt, pepper and sugar.