Heat the oil and flour in a saucepan over medium heat. Mix well and cook until lightly browned. Mix in the water. Stir until smooth. Add the bay leaf and garlic. Bring to a simmer and cook for 10 minutes.
Brown the lamb slices in a dry, nonstick frying pan over high heat. Finish the cooking in the oven. Remove the pan when the meat is about 43°C in the center. Set the meat aside, covered, to rest for 8 to 10 minutes before serving.
Place the lamb slices on individual heated serving plates. Spoon the sauce over the lamb.