Clean, wash and dice eggplant. Fry in a pan with enough hot frying oil to cover the eggplant until golden brown (check oil temperature with a piece of eggplant). Remove the eggplant with a slotted spoon and drain on paper towels.
Rinse salt-packed capers under running water. Soak raisins in warm water for 20 minutes, drain and squeeze out excess water. Heat 1/4 cup extra virgin olive oil in a pan over medium heat. Add the thinly sliced onion and sauté until golden. Stem, seed, core and dice the red pepper and add to the onion.
When soft, stir in washed and diced zucchini and cook for 3 or 4 minutes. Add the capers, raisins, pine nuts, chopped pistachios and fried eggplant. Combine with the sugar and white vinegar. Cook until vinegar is absorbed (a few seconds).
Set Caponata aside to rest in a warm place. The tuna steak should be at least 1/8-inch thick to cook properly. Season the steak with salt and pepper. Heat the remaining 1/4 cup oil in a pan over medium heat. Peel and crush the garlic with a knife and sauté.
Remove as soon as golden, place the tuna steak in the pan and sauté 1 - 2 minutes on each side, depending on how rare you like it. Serve whole or sliced with caponata.