Preheat the oven to 425 degrees F.
Place eggplant on a rimmed baking sheet; drizzle with olive oil. Sprinkle with salt and pepper. Mix together and spread eggplant out in an even layer.
Place the tray in the oven and bake for 20 minutes. Remove from the oven and set aside.
Heat 1 tablespoon olive oil in a heavy skillet over moderately high heat.
Add the chopped onion to the pan and cook, stirring occasionally until translucent, about 6 to 8 minutes.
Add the celery and garlic and cook, stirring for another 6 minutes.
Add the olives, capers and sugar and cook, stirring, 2 minutes.
Stir in the vinegar and tomatoes and bring to a boil, stirring often.
Reduce heat and simmer, stirring occasionally for 15 minutes.
Stir in the roasted eggplant and cook for 5 minutes more.
Remove pan from the heat and let cool. Transfer the caponata to a serving bowl. Serve immediately or refrigerate to use the next day.