Brush both sides of the bread with 2 tablespoons of the oil and season liberally with salt and pepper. Arrange on a rimmed baking sheet and toast in the oven until crisp and golden brown, 10 to 12 minutes. Remove to a plate.
Increase the oven temperature to 425 degrees F. On the same baking sheet, toss the grapes with the remaining 1 tablespoon oil and season liberally with salt and pepper. Roast until the grapes are starting to burst and slump, 20 to 25 minutes.
To serve, spread the cheese on the toasts and top with the roasted grapes. Sprinkle with the hazelnuts and drizzle with vinegar.
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