To roast the eggplants, preheat a charcoal or gas grill or a broiler. Alternatively, you can simply use the open flame of a gas burner.
Roast the eggplants, turning as needed, until the skin is charred on all sides. The time will vary depending on the cooking method you choose. The eggplant is cooked when it is soft and looks somewhat deflated. Place it on a plate to cool.
Trim and seed the pepper, then cut into ¼-inch dice. Cut the cucumber lengthwise in half, scoop out the seeds with a spoon, and cut into ¼-inch dice. Peel and finely chop the onion. Peel and finely chop the garlic.
When the eggplant is cool enough to handle, remove as much of the skin as possible along with any large, dark seeds. Cut the eggplant into 1-inch squares (or smaller if using it as a spread) and place it in a colander in the sink or over a bowl for 5 to 10 minutes, or until you are ready to serve, to allow the excess liquid to drain.
Transfer the eggplant to a bowl and add the pepper, cucumber, onion, and garlic. Stir in the olive oil and lemon juice and season with salt and pepper. Serve at once or the salt will draw out too much moisture from the vegetables.