Preheat the oven to 450°. Using a toothpick, pierce the eggplants all over. Place the eggplants on a rimmed baking sheet and brush with olive oil. Roast for 30 minutes, turning once, until the skin has blackened and the eggplants are tender. Slit one side of the eggplant and transfer to a colander to drain; let cool completely. Peel the eggplants, discard the seeds and cut into 1/2-inch dice.