The green, brown and puy varieties of lentils are better at keeping their shape after being cooked but if they are overcooked or over-mixed, they can break down and combine with other ingredients. If using in a salad, don't overcook and be sure to stir gently with salad ingredients. The red and yellow or golden lentils will go mushy once cooked but you can stop cooking earlier in order to have slightly less mushy lentils, although they’ll still blend into other ingredients.