For the salsa verde: Finely chop 1 garlic clove in a food processor. Add the parsley, cilantro, mint and the capers, if using. Pulse to form a coarse mixture. Transfer to a medium bowl and stir in the lemon juice, 1/4 teaspoon salt and 1/8 teaspoon pepper, then stream in 1/2 cup oil, whisking constantly. Taste, and add more salt and/or pepper as needed. The yield is about 1 cup. Cover with plastic wrap and chill for at least 1 hour or up to overnight.
For the eggplant: Preheat the oven to 375 degrees. Line a rimmed baking sheet with parchment paper.
Cut the eggplants in half lengthwise, keeping the stems on. Make several slashes diagonally across the flesh, 1/2 inch apart, scoring two-thirds of the way through the flesh without puncturing the underside skin.
Combine 2 garlic cloves and 1/3 cup oil in a small bowl, then spoon about a tablespoon over each eggplant half, working the mixture into the cuts. Brush it lightly on the skin side, too.
Arrange the eggplant halves cut sides up on the prepared baking sheet. Sprinkle the flesh lightly with salt and pepper, then drizzle with the remaining garlic-and-oil mixture to coat. Roast until the flesh is golden brown and tender, about 40 minutes.