Cook the egg in boiling water for 8-10 minutes. Rinse cold, peel and slice. Drain the tuna. Meanwhile cut the ciabatta lengthwise in half and cut each half into about 4 triangles. Mix crème fraîche and mayonnaise and season with salt and pepper. Spread the ciabatta triangles with it.
Cut the tomatoes into eighths. Peel and thinly slice the onion. Cover ciabatta with tuna, slices of egg, tomatoes, onions and olives and sprinkle with cheese. Bake in the preheated oven (electric cooker: 200 °C/ gas: level 3) for 10-12 minutes. Serve garnished with basil and olives