Fresh hazelnuts are wonderfully sweet and juicy. They have a short season, from mid-August until October, but are worth using for this salad if you can get them. Try them first and decide for yourself whether you want to roast them as I describe, or keep fresh. With or without hazelnuts, this makes the most luxurious summer starter.
Preheat the oven to 300 degrees. Scatter the hazelnuts over a baking sheet and roast for 12-15 minutes, or until nicely browned. Let them cool down before chopping roughly or just crushing lightly with the side of a large knife.
Place a ridged griddle pan on a high heat and leave it there until it’s almost red-hot — at least 5 minutes.
Meanwhile, trim the ends of the zucchini and cut them on an angle into 3/8-inch-thick slices. Place them in a bowl and toss with half the olive oil and some salt and pepper. Place the slices in the hot grill pan and char-grill for about 2 minutes on each side; turn them over using tongs. You want to get distinct char marks without cooking the zucchini through. Transfer to a mixing bowl, pour over the balsamic vinegar, toss together and set aside.
Once the zucchini have cooled down, add the remaining olive oil, the basil and hazelnuts. Mix lightly and then taste and adjust the seasoning accordingly. Transfer the salad to a flat plate, incorporating the Parmesan, and drizzle over the hazelnut oil.