Sicilian Eggplant and Tuna Salad (Caponata alla Siciliana)

Ingredients

• ¾ cups extra-virgin olive oil
• 2 medium eggplants, trimmed, peeled, and cut into small cubes
• 3 stalks celery, trimmed and coarsely chopped
• 1 medium yellow onion, peeled and chopped
• Salt and freshly ground black pepper
• 1 medium tomato, coarsely chopped (optional)
• ¼ cups red wine vinegar
• 1 tbsp. sugar
• ¾ cups capers
• 1 tbsp. pine nuts
• 1 6 oz. oil-packed tuna, drained and broken up with a fork
• ½ bunches parsley, finely chopped