For the gratinated pollock with cocktail tomatoes, rinse the pollock with cold water, pat dry and sprinkle with lemon juice. Place the fish fillets in a baking dish, season with salt and pepper and brush with mustard.
Cut young onion into small rings, quarter tomatoes. Mix crème fraîche with oregano, onions, tomatoes and breadcrumbs.
Spread this mixture on the fish fillets and sprinkle with grated cheese. Bake in the preheated oven at 180 °C for about 30 minutes.