How to Make It
In a medium saucepan, combine the tomatillos, onion, jalapeño and garlic with 1 cup of water and bring to a boil. Simmer over moderate heat until the vegetables are softened, about 8 minutes. Using a slotted spoon, transfer the vegetables to a blender.
Boil the cooking liquid until reduced to 1/4 cup, then add it to the blender and let cool completely. Puree the salsa and season with salt and pepper. Transfer the salsa to a bowl, stir in the chopped cilantro and refrigerate until chilled, about 45 minutes.
Meanwhile, in a bowl, toss the celery with the lime juice; season with salt and pepper.
Light a grill or preheat a grill pan; oil the grill grate. Thread 3 shrimp onto each skewer. Brush the shrimp with olive oil and season with salt and pepper. Grill over high heat, turning once, until lightly charred and cooked through, about 4 minutes. Remove the shrimp from the skewers and transfer to a platter. Serve the shrimp with the salsa, celery salad, warm tortillas, cabbage and parsley leaves so guests can assemble their own tacos.