Bilad al-Sham Kitchen - Fish fillet with green dressing and tomatoes

Fish fillet with green dressing and tomatoesFor thickness:A kilo of fish filletA quarter cup of olive oilA spoonful of mustardA spoonful of fish seasoningSalt and PepperMarinade:

Two cups of chopped parsley5 grains of garlicHalf a cup of olive oilQuarter cup of lemon juice3 grains of tomatoChopped large onion