Rinse the lentils under cold water and drain.
Peel and finely dice the shallot and carrot.
Pat the mozzarella dry, halve and thinly slice.
Mix together the vegetable stock, oil, 2 tbsp vinegar and the mustard. Season with salt and pepper.
Wash the chives and shake dry. Reserve a few stalks and finely chop the rest.
Mix the lentils, shallot, carrot and chives with the marinade. Season with salt, pepper and the remaining vinegar.
Toss the salad with the mozzarella and garnish with the remaining chives. Toast the bread until crisp and serve on the side.