How to Make It
Using small scissors, cut lengthwise down the back of each shrimp shell; remove and discard vein. (Do not remove shells.) Rinse shrimp with water, and pat dry. Stir together shrimp, 2 tablespoons oil, and 3/4 teaspoon salt in a bowl.
Preheat grill to medium-high (400°F to 450°F). Place a large cast-iron skillet on grill grates. Cover grill; let skillet preheat 5 minutes. Uncover grill; add remaining 2 tablespoons oil to skillet. Add shrimp; cook, uncovered, turning occasionally, until shrimp begin to turn pink, 2 to 3 minutes. Add garlic and crushed red pepper; cook, stirring occasionally, until garlic is golden, shrimp are cooked through, and shrimp shells are beginning to crisp, 3 to 4 minutes.
Remove skillet from grill; immediately transfer shrimp to a serving platter. Cut lemon in half; squeeze 1 lemon half over shrimp (discarding seeds). Sprinkle shrimp with cilantro and remaining 1/4 teaspoon salt. Cut remaining lemon half into wedges, and serve with shrimp.