Line a heavy large baking sheet with foil. Cut cross-hatch marks over the cut side of the eggplants. Arrange the eggplants and the Roma tomatoes cut side up on the prepared baking sheet. Brush with 2 tablespoons of oil. Sprinkle with salt and pepper.
Whisk 2 tablespoons of oil, 2 teaspoons of garlic, and 1/4 teaspoon of oregano in a small bowl to blend. Stir in the diced tomatoes. Season with salt. Spoon the oil mixture over the eggplants. Sprinkle the eggplants with salt and pepper.
Stir the bread crumbs, remaining 2 tablespoons of oil, 2 teaspoons of garlic, and 1/4 teaspoon of oregano in another small bowl to blend. Sprinkle the bread crumb mixture over the Roma tomatoes.
Bake until the vegetables are tender and the bread crumb topping is brown, about 30 minutes.