Defrost the puff pastry. Clean, wash and slice the zucchini. Peel and finely chop the onion. Heat oil in a large frying pan. Add the zucchini and fry well.
Add the onion and fry briefly. Season with salt and pepper and let it cool down a bit. Rinse salmon, dab dry and cut into cubes. Sprinkle with lemon juice. Grate cheese finely. Mix eggs and sour cream.
Season with salt and pepper. Place the puff pastry slices on top of each other and roll out round (approx. 32 cm Ø). Line a quiche tin (approx. 26 cm Ø) with the dough, press up at the edge so that it protrudes approx. 1 cm over the edge.
Prick the pastry base several times with a fork and let it rest for about 10 minutes. Sprinkle the dough with breadcrumbs. Spread zucchini and salmon on top. Pour the souring mixture over it. Sprinkle with cheese. Bake in the preheated oven on the lower rack (electric oven: 200 °C/ convection oven: 175 °C/ gas: level 3) for 40-45 minutes.
Possibly garnish with dill.