Wash the eggplant well and cut it in half lengthwise.
Cut away 2 to 3 millimeters (1/16 inch) of the skin along the side edges.
Cut slashes through the flesh but not through the skin. This will facilitate the cooking of the flesh and later removal of the skin.
Heat oil to 177°C (350°F) in a deep-fat fryer.
Drop the eggplant halves into the hot oil and cook for about 5 minutes or until the skin easily pulls away from the flesh. (Alternatively, the eggplant halves may be brushed with oil and placed, cut side down, in a preheated 177°C (350°F) oven and baked for about 30 minutes or until very soft.)
Remove the eggplant from the hot oil and place on a double layer of paper towels to drain.
Preheat the oven to 177°C (350°F).
Scoop out the interior flesh and set aside the flesh and the skin separately.
Chop the eggplant flesh.
Finely dice (ciselé) the onions.
Heat olive oil in a sautoir over medium heat.
Add the onions and sauté until they have sweated their liquid but not taken on any color. Season to taste with salt and pepper.
Add the chopped eggplant and cook, stirring to combine. Return the eggplant mixture to the reserved skins.
Place the filled eggplant halves in the oven and bake for 15 minutes or until nicely browned.
While the eggplant is baking, cut enough 7 millimeters (¼ inch) thick tomato slices to cover the top of each eggplant half.
Sauté the tomatoes in olive oil for about 3 minutes to just cook slightly.
Place the tomato slices on the baked eggplant and serve hot or at room temperature.