Heat oven to 425 degrees. Trim eggplants and cut in half lengthwise; season cut sides with salt and pepper. Coat a large roasting pan with olive oil (1 to 2 tablespoons). Arrange eggplants cut side down; sprinkle with more salt and pepper. Roast for 25 minutes on the first side, or until brown underneath then flip and roast 5 to 10 minutes more. Remove from oven and let cool slightly.
Meanwhile, make couscous, if using it. Bring 3/4 cup water and a few pinches of salt to a simmer then pour it over dried couscous in a bowl. Cover with a lid or foil and let side for 5 minutes to absorb, then fluff with a fork.
Make tomato relish by pulsing garlic and parsley in a blender or food processor until finely chopped, then add tomatoes and pulse until they’re well chopped. Add 1 tablespoon olive oil, vinegar, salt, freshly ground black pepper or a pinch or two of red pepper flakes and pulse to combine. No food process or blender? Not a problem at all; just mince the garlic and parsley well and finely chop the tomatoes; stir this together with the remaining ingredients. Both methods: taste for seasoning. We like this extra sharp and almost always add 1 more teaspoon vinegar and more salt. The longer it sits, the more potent it gets.
To assemble, schmear each eggplant half with a little yogurt. If you’re using couscous, sprinkle a little on top. Spoon tomato relish over and serve the rest of all the above on the side.