Clean or peel the soup greens and cut into pieces or rings. Heat 1 tablespoon of olive oil in a pot. Add carrots, celery and leek and fry for 2-3 minutes. Add stock, bring to the boil and simmer for 6-8 minutes.
Add the lentils and simmer for another 8-10 minutes. Puree the soup lightly. Season to taste with salt, pepper and vinegar.
In the meantime, peel and finely chop the garlic for the Gremolata. Wash parsley and mint, shake dry, pluck off leaves and chop finely. Wash lemon hot, grate dry and grate peel thinly.
Mix chopped herbs, garlic and lemon peel and chill until ready to use. Halve the lemon and squeeze one half.
Wash the fish, dab dry and cut into pieces. Season with salt and pepper. Sprinkle with lemon juice. Heat 2 tablespoons of olive oil in a coated frying pan. Sauté the fish for 4-5 minutes on the skin side first.
Turn the fish and finish cooking in 2-3 minutes.
Arrange the soup in bowls or deep plates. Spread fish fillets on top and sprinkle Gremolata on top.