Cut the eggplant and zucchini into chunks (no need to peel).
Heat the oil in a large pan, then add the eggplant and zucchini and fry for 5 minutes or until soft. You may need to cook them in batches if your pan isn't large enough. Remove the eggplant and zucchini and set aside.
Add the celery, onion and garlic to the pan (don't clean it out first) and cook for a few minutes until soft but not browned.
Add the tomatoes, capers, olives, vinegar, sugar and chocolate. Season with pepper (there is already salt from the capers and olives) and bring to the boil, then reduce the heat and stir in the cooked eggplant and zucchini. Cover the pan with a lid ad cook for 15 minutes, stirring occasionally.
To serve as an appetizer, cut the baguette into 1/4 inch thick slices and toast each side, then rub each one with the cut clove of garlic. Pile each slice with a tablespoon of the caponata (warm or cold) and top with a sprig of basil and a drizzle of oil. Don’t add the caponata until just before serving.
If making bruschetta/crostini don’t add the caponata to the toast until just before serving.