In a 5- to 6-quart nonstick pan over high heat, bring 2 1/2 to 3 quarts water to a boil. Meanwhile, rinse beans; trim off stem ends and discard. Cut beans into 3-inch lengths. Rinse, stem, and seed bell pepper; cut into thin slivers 2 to 3 inches long.
Add beans to boiling water and return to a boil. Remove from heat and add bean threads and scallops; cover and let stand until scallops are barely opaque in center of thickest part (cut to test) and bean threads are barely tender to bite, 3 to 5 minutes. Drain, rinse with cold water until cool, and drain again thoroughly. Rinse and dry pan.
In same pan over high heat, stir garlic and ginger in oil just until garlic begins to brown, about 1 minute. Stir in chile flakes and remove from heat. Add soy sauce, vinegar, and sugar. Add noodle mixture, bell pepper, and green onions; mix gently. Mound on dinner plates or pour into a wide serving bowl.
Four types of noodles: Look for dried Asian noodles in the international section of the supermarket or in an Asian market.
Bean threads (saifun or cellophane noodles). Thin, wiry dried noodles, made from the starch of mung beans, turn clear and slippery when cooked in water or puffy and crisp when deep-fried. Neutral flavor.
Rice noodles (rice sticks, mai fun, mi fun). Dried white noodles, made from rice flour, vary from whisker-thin to about 1/4 inch wide. When cooked in water, they turn opaque and tender; when fried, they puff and crisp. Mild rice flavor.
Soba. Buckwheat and wheat flour infuse thin, tan Japanese noodles with robust, earthy flavor.
Wheat noodles (Chinese noodles or Oriental noodles, mein). Available in many forms, these all-purpose noodles taste similar to spaghetti and go by many names.