1. Preheat the oven to 425°F (210°C). Blanch, peel, and remove the seeds from the tomatoes. Coarsely chop the pulp. Peel the garlic cloves and crush them using a garlic press or the flat side of a knife blade.
2. Peel and finely chop the onion. In a thick-bottomed sauté pan, gently sauté the chopped onion and garlic in olive oil until translucent.
3. Add the chopped tomatoes and chopped tarragon, season with salt and pepper, and simmer for 15 minutes. Meanwhile, wash and dry the eggplants. Cut them into thick and even slices.
4. Brush them with the remaining olive oil using a brush. Brown them in the oven on a non-stick baking sheet for 5 minutes on each side. Remove them from the oven and set them aside. Drain the mozzarella and cut it into thin slices.
5. Cover the eggplant medallions with a slice of mozzarella, drizzle with the tomato reduction, and bake for 5 minutes.
6. Arrange the medallions on plates, surround them with a drizzle of cooking sauce, and garnish with oregano. Serve immediately.