Grilling the eggplant adds a charred note to this classic Middle Eastern dip. Let the slices steam after cooking so the flesh becomes even more tender. Serve with toasted pita, sliced cucumber, or fennel.
Preheat grill to high.
Cut eggplant into 1/2-inch-thick slices; coat with cooking spray. Arrange slices on grill rack; grill 10 minutes or until tender, turning after 5 minutes. Place eggplant in a bowl; cover with plastic wrap. Let stand 5 minutes. Place eggplant, 3 tablespoons oil, tahini, juice, 1 tablespoon oregano, and remaining ingredients in a food processor; pulse until smooth. Place mixture in a bowl; drizzle with remaining 1 tablespoon olive oil. Sprinkle with remaining 1 1/2 teaspoons oregano.