Prepare a grill, indoors or outdoors. Grill the bread on both sides until toasted. You may have to do this in two or more batches. Alternatively, use a toaster to toast bread. Mix olive oil with garlic. When bread is toasted, lightly brush olive oil and garlic mixture on one side of each piece of grilled bread. Spread a thin layer of robiola on each slice and top with thinly sliced prosciutto. In a small bowl, combine tomatoes, red onion, basil and olives. Spoon on top of bread slices and drizzle with balsamic vinegar, if desired.