Slice the courgettes lengthwise and parboil for a few minutes in salted water.
In a bowl, combine the breadcrumbs with grated Grana Padano, chopped chives, lemon zest, salt and pepper.
Cut the flounder fillets lengthwise and sprinkle with the Grana Padano mixture. Top with a slice of courgette and roll it up, holding the roll closed with a toothpick.
Arrange on a baking sheet lined with parchment paper, drizzle with oil and bake in a preheated oven at 180 °C for 10-15 minutes.
Serve the rolls hot.