To make the pesto, combine basil, garlic, and pine nuts in a food processor. Add half of the oil and blend until finely chopped. Add parmesan cheese and blend again, adding oil until the pesto reaches a spoonable consistency. Season with salt and pepper.
To make the balsamic glaze, reduce the vinegar over medium-low heat until it is thick enough to coat the back of a spoon. Turn off heat and whisk in sugar.
Combine diced tomatoes with one tablespoon of pesto per tomato.
Toast bread slices on the grill or in the oven, then rub each slice with a whole garlic clove.
Top each slice of bread with a hearty spoonful of tomato–pesto mixture and drizzle with balsamic glaze.
