Mix together the brown sugar, chipotle, 1 teaspoon salt and 1/2 teaspoon black pepper in a small bowl. Rub into the steaks and set aside for 15 minutes.
While the steak rests, crush the garlic clove, sprinkle with a pinch of salt, and mash into a coarse paste using flat side of a large knife. Mix the garlic paste with the cilantro, oil, habanero, mango, lime juice and scallions in a medium bowl. Season with salt and as much of the remaining habanero as desired for spiciness. Set aside.
Lightly oil the grill grates. Grill steaks until well charred on the outside and medium-rare, about 2 1/2 minutes per side. Set aside to rest for 5 minutes then slice steaks across the grain and serve with the mango salsa and a lime wedge.
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