Preheat the grill to medium. Lightly toast the bread slices on both sides under the grill. Top each toast with a slice of brie then cook under the grill until the cheese has melted and is just bubbling. Set aside.
Combine the salad leaves in a large salad bowl. Add the radishes, peaches and about 2/3 cup (100g) of the redcurrants or blueberries.
Put the remaining redcurrants or blueberries in a small bowl, add the oil and, using a fork, lightly crush the fruit. Stir in the vinegar and season to taste.
Pour the dressing over the salad and toss together well to mix. Scatter with the toasted hazelnuts and arrange the brie crostini on top. Serve immediately.