3 tablespoons unseasoned rice vinegar
2 tablespoons finely grated peeled fresh ginger
2 tablespoons peanut oil
2 tablespoons Asian sesame oil
2 tablespoons soy sauce
2 tablespoons honey
1 tablespoon chopped fresh cilantro
1 serrano chile, seeded, minced
Freshly ground white pepper
1 1/2 pounds 1 1/4 -inch-thick ahi tuna, cut into 1- to 1 1/4 -inch cubes
Nonstick vegetable oil spray
1 large red bell pepper, cut into 1-inch squares
1 large sweet onion (such as Maui or Vidalia), cut into 1-inch squares
6 (12-inch-long) metal skewers
Additional chopped fresh cilantro