Soak bamboo skewers in water for 1/2 hour. Thread 5 shrimp onto each skewer, threading each shrimp through the tail end and then again through the head end; arrange on a large plate. In small bowl, whisk oil, cilantro, lime juice, garlic, black pepper, salt, red pepper flakes, and chili powder  until combined; rub over shrimp. Marinate 30 minutes, refrigerated, turning once.

For the Mango Salsa: In medium bowl, combine all salsa ingredients. Let stand at room temperature while shrimp are marinating.

Prepare an outdoor grill or preheat stovetop grill pan over medium-high heat. Grill shrimp 2-1/2 to 3-1/2 minutes per side until just cooked through (shrimp will be just barely opaque in thickest part when cut with a knife).  Serve with salsa.