Cook the lentils in the broth for about 30 minutes. If you have time, you can soak the lenses overnight, but this is usually not necessary. Don`t use red lentils, they`ll get mushy. Broth makes the lentils spicier and, in my experience, doesn`t stay hard even with salt.
In the meantime, quarter the cocktail tomatoes and cut the spring onions into fine rings.
Mix a vinaigrette from the other ingredients (possibly also add mustard). Mix the drained, cooked, slightly cooled lentils with the tomatoes and onions in the sauce.
Tastes lukewarm and cold with meat and pan-fried fish fillet or something like that. Can be well prepared for a party a day in advance.