Clean and wash spring onions and cut into wide rings. Mix sour cream and thyme and season with salt and pepper. Cut the dough in half crosswise. Roll out both halves one after the other on a floured work surface.
Place on 2 baking trays lined with baking paper. Spread half of the sour cream on each tray. Spread the spring onions and tuna on top. Bake one after the other in a preheated oven (electric cooker: 225 °C/ convection oven: 200 °C/ gas: level 4) for about 5 minutes.
Remove and cut in half.