In a medium bowl, whisk together the lime juice, palm sugar (or brown sugar), scallions, shallots, jalapenos, fish sauce, garlic and sesame oil.
Preheat a grill to high. Transfer 1/2 cup of the vinaigrette to a large bowl; whisk in the grapeseed oil. Add the shrimp, season with pepper and toss to coat. Grill the shrimp, flipping halfway through, until just cooked through, 2 to 3 minutes per side.
Transfer the shrimp to a platter; drizzle with some of the remaining vinaigrette. Serve with the lime wedges.