1. Chop peppers, removing seeds for less intense heat if desired. Add all marinade ingredients to a blender and blend until incorporated. In a ziplock bag, combine shrimp and enough marinade to completely cover (about ¾ of the mixture). Reserve the remaining marinade for the final step. Flip bag over several times to fully coat the shrimp. Refrigerate for at least 2 hours.
2. After marinating, thread shrimp onto wet bamboo or metal skewers, alternating with pineapple and red bell pepper.
3. Preheat the charbroiler for 10 minutes on medium-high heat. Grill about 3 minutes per side.
4. Transfer to a platter and spoon the reserved marinade over the cooked shrimp. Top with scallions, if desired.