In a small bowl, combine the cumin, cardamom, salt, and pepper.
In 1 large non-stick skillet, working in batches, heat 2 tablespoons of the oil in each pan over moderately high heat until it is hot but not smoking. Add half the onions and half the tomatoes in one layer to each pan, and cook for 3 minutes.
Turn the vegetables over, sprinkle them with the spice mixture, and cook until they are just tender, about 3 minutes more. Divide the vegetables between 4 heated plates, placing 2 slices of each vegetable per plate.
To each skillet, add 1 tablespoon oil per pan. Pat the lamb chops dry, season with salt and pepper, and saute, 4 in each pan, over moderately high heat, for 5 minutes on each side, for medium-rare, and arrange them on top of the vegetables.