Place the grapes and honey in a small saucepan and bring to a boil. Season with salt and pepper. Reduce the heat and simmer until the grapes are tender, about 10 minutes. Remove from the heat, add the tarragon and let cool. Drain.
With the rack in the top position, preheat the broiler.
Arrange the baguette slices on a baking sheet. Top with cheese. Broil until the cheese melts and the bread turns golden, about 2 minutes. Arrange 3 grapes on each toast. Serve immediately.