Give your flank steak a sweet and spicy kick with a delicious rub made from a blend of different chili powders, cumin, brown sugar and thyme. Finish it off with a squeeze of fresh lime when it comes off the grill.
Grate the zest of 1 lime; cut the lime in half. Combine zest with the chili powder, brown sugar, thyme, cumin, chipotle powder, 1/2 teaspoon salt and a few grinds of pepper in a small bowl. Squeeze the zested lime over the steak and use the lime halves to rub the juice into the meat. Rub the spice mixture on both sides of the steak. Let stand at room temperature, 30 minutes.
Meanwhile, preheat a grill to medium high. Brush the grates with vegetable oil. Grill the steak until well browned, about 8 minutes. Flip and grill until a thermometer inserted sideways into the center registers 130 degrees F to 140 degrees F, 5 to 7 more minutes for medium rare (the thinner edges of the steak will be cooked to medium).
Transfer to a cutting board and let rest 10 minutes. Season with salt and thinly slice against the grain. Serve with lime wedges.