Soak the lentils overnight in plenty of cold water.
Wash the meat, dab dry, cut the skin with a sharp knife into thin strips. Season with salt. Place meat with the skin side first in a cold pan and fry over medium heat for about 5 minutes.
Turn and fry on the meat side for another 3 minutes. Remove from the pan and cook in a casserole dish in a preheated oven (electric range: 150 °C/ convection oven: 125 °C/ gas: see manufacturer) for approx. 12 minutes.
In the meantime, read out the spinach and rocket. Wash spinach, rocket and parsley, shake dry. Roughly chop the rocket. Pluck parsley leaves from the stalks and chop. Peel and chop onions and garlic.
Drain the lenses, rinse and drain.
Heat the oil. Briefly sauté the onions and garlic in it until transparent. Add lentils and stock. Add spinach, rocket and parsley and let them collapse. Season to taste with salt, pepper and lemon juice.
Cut the duck into slices. Arrange herb lentils and meat. Yoghurt tastes good with it.