Defrost the scallops if necessary. Grate cheese. Heat 2 tablespoons of oil in a pan. Fry the baguette in it until light brown on each side, season with salt and remove. Let it cool down.
Wash, quarter, seed and dice the tomatoes. Wash parsley and shake dry. Chop the leaves. Mix tomato cubes, 1 tablespoon of oil and parsley. Season to taste with salt, pepper and vinegar.
Rinse mussels cold and dab dry. Heat 1 tablespoon of oil in a frying pan. Fry the mussels for 2-3 minutes, turning them over. Season with salt and pepper and remove.
Preheat the oven grill. Place the baguette on a baking tray. Spread tomatoes on top. Put 2 mussels on each. Sprinkle with cheese. Bake for about 3 minutes until the cheese has melted. Take out and arrange immediately.