Preheat a grill pan over medium-high heat.
Put the lamb chops in a bowl, drizzle a couple of tablespoons oil over them along with the fennel seeds, and salt and pepper and toss well to coat the meat. Let stand 10 minutes.
Slice one of the star fruit, remove the seeds, and transfer to the bowl of a food processor or blender. Add the rice vinegar and puree the fruit until fine. Pour the mixture into a small saucepan, add the brown sugar and garlic and season with salt and pepper. Bring to simmer and cook until the liquid is evaporated and the mixture is thick, about 10 minutes. Add a splash of water if the pan gets dry. It should be the consistency of drained crushed pineapple.
Slice the leeks in half lengthwise, then slice crosswise into 1/4 inch pieces. Heat 1 tablespoon of oil in a large skillet over medium-high heat, add the leeks, season with salt and pepper, and cook, stirring, until beginning to brown, about 6 minutes. Add the red onion and cook. stirring, until onion is translucent, another 3-4 minutes. Carefully add the wine and simmer until the liquid has evaporated; add the butter, stir until melted and combined and remove from the heat.
Shake any excess fennel seeds from the lamb and place on the grill pan; cook, turning once, until grill marks appear, and meat is medium-rare, 3-4 minutes per side. Let stand 5 minutes before serving. While the lamb is cooking, slice the remaining star fruit and grill briefly on both sides.
To serve, put 2 lamb chops on each of two plates and spread a little of the star fruit relish on each chop; divide the leeks between the plates, and serve with hot Eggplant Rollatini and garnish the plate with grilled star fruit slices.