Preheat oven to 375° F.
In a medium bowl, whisk olive oil, vinegar and all spice. Add grape halves and onion; toss to coat then spread over a large rimmed baking sheet. Roast grapes in oven until slightly soft, about 8 to 10 minutes. Remove baking sheet onto wire rack to cool. Turn oven to broiler.
Meanwhile, place pine nuts in a small skillet over medium heat, shaking skillet often until pine nuts are golden all over, about 4 minutes.
Arrange bread slices in an even layer onto another baking sheet. Top evenly with gorgonzola; broil until cheese melts slightly and bread is toasted, about 2 to 3 minutes.
To serve, use a slotted spoon top each bread slice with the roasted grape mixture. Sprinkle with toasted pine nuts. Add fresh cracked black pepper, to taste.