How to Make It
In a large, deep skillet, heat 1/4 cup of the olive oil. Add the zucchini, bell pepper, onion, thyme and sliced garlic and season with salt and pepper. Cook over high heat, stirring occasionally, until the vegetables are crisp-tender, about 7 minutes. Add the tomato, fennel, olives and capers, season with salt and pepper and cook, stirring, until the vegetables are tender, 2 to 3 minutes longer. Discard the thyme.
In a medium skillet, heat the remaining 1/4 cup of oil with the halved garlic cloves. Season the tuna with salt and pepper, add it to the skillet and cook over moderate heat for 3 minutes, turning once. Cover the skillet and cook the tuna over very low heat for 2 minutes longer; the tuna should still be slightly rare in the center.
Spoon the vegetables onto plates. Top with the tuna steaks and the browned garlic halves and serve.