Bring a medium saucepan of water to a boil, and cook the asparagus until tender but crisp. Drain, and briefly immerse in cold water.
In a large, resealable plastic bag, mix the rice vinegar, soy sauce, vegetable oil, sugar, salt, and pepper. Seal the asparagus in the bag. Marinate 24 hours in the refrigerator. Sprinkle the marinated asparagus with pecans and green onion to serve.
