Place the grape bunches on a baking sheet and drizzle with balsamic vinegar and olive oil. Season with salt and pepper. Toss to coat the grapes evenly.
Roast the grapes in the oven for about 15-20 minutes, until they are slightly shriveled and caramelized but still hold their shape.
While the grapes are roasting, arrange the baguette slices on a separate baking sheet and brush them lightly with olive oil. Toast in the oven for about 5-7 minutes, until golden and crispy.
In a small bowl, mix the softened goat cheese with honey until creamy and well combined.
Once the grapes are done roasting, remove them from the oven and allow them to cool slightly.
To assemble the crostini, spread a generous layer of the honey-goat cheese mixture over each toasted baguette slice. Top with a spoonful of roasted grapes and a sprinkle of fresh thyme leaves.
Serve immediately while the crostini are still warm.