Using a parisienne scoop, remove balls of flesh from the zucchinis until only the shells are left. Keep the zucchini balls aside.
2 zucchinis
Preheat a grill to medium-high.
On a large skillet over medium-high heat, warm up 1 tbsp. of the olive oil and cook the onions in it for 3 to 4 minutes.
1 onion, 3 tbsp. olive oil
When the onions are soft, add the garlic and cook for a minute. Add the remaining olive oil, the cubed eggplant, and the zucchini balls. Cover and cook for around 8 to 10 minutes.
1 small eggplant, 2 garlic cloves
Add the tomatoes and cook for another 5 minutes, stirring frequently. Stir in the parsley and season with salt and pepper to taste.
2 tomatoes, Sea salt and freshly ground black pepper
Fill each zucchini shell with the ratatouille. Grill for 2 to 3 minutes (or until the zucchini shells get soft) and serve hot.