In a sauce pan heat balsamic vinegar over medium heat. Stir in sugar.

Bring to a boil then lower heat to a simmer. Occasionally stir and simmer until vinegar is reduced by about half and vinegar thickens (about 20 minutes).

In a small bowl mash avocados and add lemon juice, salt and pepper.

Spread avocado on each flatbread then layer tomato slices, mozzarella slices, basil leaves and top with balsamic glaze.