Heat one large cast-iron pan over high heat. Let the pan get very hot before adding the oil. once you do add the oil, wait for it to shimmer before you put the tuna steaks in the pan, cumin-side up. Cook 3–4 minutes and turn. Cook the cumin side for only one minute. Transfer to a plate and place 1 tablespoon of the Jalapeno-Cumin butter on each steak before resting it for 3 minutes in the 175° degree warming oven. Finish with a squeeze of lime.