Whisk oil, cilantro, lime zest, lime juice and salt in a large bowl. Set aside 3 tablespoons of the mixture in a small bowl to use as dressing. Add shrimp, jalapenos and plums to the remaining marinade; toss to coat.
Preheat grill to medium-high.
Make 4 kebabs, alternating shrimp, jalapenos and plums evenly among the skewers. (Discard the marinade.) Grill the kebabs, turning once, until the shrimp are cooked through, about 8 minutes Total. Drizzle with the reserved dressing.