Make the marinade: Peel the onion and cut into rings. Wash the lemon, cut it along with the zest, first in half lengthwise, and then into slices. Wash greens, dry and finely chop. Add vegetable oil, cognac, black pepper and herbs to the onion and lemon. Pour the marinade over the fish and let it brew for 30 minutes. Grill marinated fish pieces for 3-5 minutes. from each side.
* If red fish is overcooked in this sauce, it will lose its color and taste.
Make the sauce: Wash the parsley, pat dry and finely chop. Peel and crush the garlic. Grind greens with garlic. Mix cheese with cream and lemon juice, add to the mixture. Cut the celery into small pieces and add to the sauce.
* You can add sliced olives to the sauce.