STEAK MARINADE:
ADD LIME JUICE, SALT, PEPPER, AND SUGAR. WHISK TO COMBINE.
TRANSFER THE MARINADE TO A ZIP-TOP BAG AND ADD THE FLANK STEAK. REFRIGERATE FOR AT LEAST 4 HOURS OR OVERNIGHT.
REMOVE THE STEAK FROM THE BAG AND DRY WITH A PAPER TOWEL. THEN, DRIZZLE THE MEAT WITH OIL AND SPRINKLE WITH SALT.
ADD REMAINING OIL TO A LARGE SKILLET OVER MEDIUM-HIGH HEAT. SEAR THE STEAK FOR 6-7 MINUTES ON ONE SIDE AND ANOTHER 4-5 MINUTES ON THE OTHER.
ALLOW TO REST 10 MINUTES. THEN SLICE THE BEEF AS THIN AS POSSIBLE.