How to Make It
Heat 3 tablespoons olive oil in a large skillet over medium. Add breadcrumbs, and cook, stirring occasionally, until golden brown, 5 to 6 minutes. Remove from heat. Stir in lemon zest and 1/4 teaspoon salt; set aside.
Cut eggplants in half lengthwise. Scoop out pulp, leaving a 1/4-inch shell. Chop pulp into 1/2-inch cubes. Sprinkle eggplant shells with 1 teaspoon salt, and invert onto a clean, dry towel. Let stand 30 minutes to drain.
Preheat broiler to high with oven rack 5 to 6 inches from heat. Pat eggplant shells dry, and brush with 1 tablespoon oil. Place eggplant shells, cut side up, on a baking sheet, and broil just until tender, about 5 minutes. Remove from oven, and reduce oven temperature to 375°F.
Heat 1 tablespoon oil in a large skillet over medium-high. Add sausage, and cook, stirring often with a wooden spoon to break up large pieces, until sausage is browned, 7 to 8 minutes. Using a slotted spoon, transfer sausage to a bowl lined with paper towels. Reserve drippings in skillet.
Heat remaining 2 tablespoons oil in skillet over medium-high. Cook reserved eggplant cubes in hot oil, stirring occasionally, until lightly browned, 2 to 3 minutes. Add onion, and cook, stirring occasionally, until just tender, 2 to 3 minutes. Add tomatoes, garlic, pepper, and remaining 1/2 teaspoon salt, and cook, stirring occasionally, until tender, 2 to 3 minutes.
Transfer tomato mixture to a large bowl. Add sausage, feta, 1/2 cup breadcrumb mixture, egg, 2 tablespoons oregano, 2 tablespoons mint, 2 tablespoons parsley, and vinegar; toss until combined. Divide mixture evenly among eggplant shells. Top evenly with remaining breadcrumb mixture, and place stuffed eggplants in a single layer in a 13- x 9-inch baking dish. Bake at 375°F until filling is golden and bubbly, 25 to 30 minutes.
Meanwhile, stir together marinara sauce, remaining 2 teaspoons oregano, remaining 2 teaspoons mint, and remaining 2 teaspoons parsley in a small saucepan. Heat over low just until warmed through, about 5 minutes. Drizzle over baked stuffed eggplant just before serving. Sprinkle with additional feta, if desired.