Ahi Cake

Put the garlic, rosemary, and thyme in a blender or food processor and puree. With the motor running, slowly add the oil. Set aside.
Preheat the broiler. Sprinkle the onions and eggplant on both sides with salt and pepper and place on a dish for 15 minutes to sweat. Pat the vegetables dry with paper towels. Place the vegetables on a grill pan and brush both sides with the garlic-herb oil. Broil the vegetables 3 inches from the heat until they are lightly browned, about 2 minutes. Refrigerate.
Sprinkle the ahi with salt and pepper. Heat a large saute pan or skillet over high heat, coat the pan with the garlic-herb oil, and sear the ahi slices for 15 seconds on each side, or until the outside is cooked and the center is still rare. Transfer the ahi to a plate and refrigerate.
To assemble: Fan half the tomato slices in a circular pattern around the bottom of a 6-cup bowl lined with plastic wrap. Layer half of the onions, basil leaves, and eggplant in the bottom of the dish. Drizzle with 1 tablespoon of the garlic-herb oil. Place half of the ahi slices over the vegetables. You may have to cut and piece the ahi to form an even layer. Repeat this process to make a second layer of vegetables, infused oil, and seared fish. For the last layer, fan the remaining tomatoes in a circular pattern over the top of the vegetables. Place a small plate upside down on top of the tomatoes and weight with a heavy, small dish or other object. Refrigerate for at least 1 hour.
To serve: Drain any juices which have accumulated. Unmold the cake. With an electric knife, carefully slice it into 8 portions and serve garnished with a basil leaf.