Stir together sliced ginger, sliced garlic, spring onions, and olive oil in a bowl. Add shrimp, toss to coat, cover, and marinate in the refrigerator 1/2 hour and up to 2 hours.
Prepare a charcoal or gas grill for high heat (you can hold your hand at grill level only 2 to 3 seconds).
Meanwhile, whisk together grated ginger, grated garlic, rice vinegar, and soy sauce in a small bowl. Thread shrimp onto soaked skewers (see notes) and season with salt and pepper.
Brush the grill with vegetable oil. If using coals, mound to one side to reach about 4 inches below the grill. Lay skewers on grill; close lid on gas grill.
Grill the shrimp until just opaque, about 1 minute per side. Serve skewers drizzled with ginger sauce.
Makes 24 miniature (4- to 4 1/2-inch) skewers