Step 1

In a dish large enough to hold the steak, whisk together the soy sauce, lime juice, vegetable oil, sugar, cumin, chili powder, and garlic.

Step 2

Using a fork, poke holes about an inch apart all over the steak on one side only. Place the steak in the marinade and turn to coat evenly (it doesn't matter which side is up). Cover and refrigerate for at least 4 hours and up to 8 hours, turning the steak at least once.

Step 3

Lightly oil the grill grates and preheat the grill to high. Grill the steak, covered, for 5 to 6 minutes per side for medium-rare. Let the meat rest on a cutting board, tented with aluminum foil, for about 5 minutes. Slice thinly against the grain and serve.

Step 4

Note: You may need to buy 2 separate flat iron steaks to get 2 pounds. Even if you're able to find one large steak, it's best to cut it in half into two smaller steaks -- they will cook faster and you'll have more surface area to char on the grill (we fight over the charred end pieces!).