Position an oven rack in the center of the oven and preheat to 350 degrees F. Bake the coconut on a rimmed baking sheet, stirring occasionally, until light golden brown, 5 to 7 minutes. Let cool.
Meanwhile, put the lime zest on a paper towel-lined microwave-safe plate and microwave in 30-second increments, stirring with a fork in between, until the zest is dry and almost brittle, 2 to 4 minutes total. (The timing will largely depend on the power of your microwave.)
Add the cooled coconut, dried lime zest, chili flakes, coriander, garlic and 1/2 teaspoon salt to a spice grinder and grind to the texture of very coarse cornmeal; reserve.
Heat the oil in a large skillet over medium-high heat. Sprinkle the shrimp liberally with salt. In two batches, add the shrimp to the skillet in a single layer and cook until lightly browned and the edges turn pink, 1 to 2 minutes. Flip and cook until the shrimp are cooked through, 1 to 2 minutes more.
To serve, sprinkle 2 to 3 tablespoons of the dried spice blend over the shrimp. (Reserve the remaining spice blend for another use. See Cook's Note below.) Garnish with the cilantro and scallions and serve with the lime wedges.
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