1. Bring a large pot of salted water to boiling. Remove from heat and add the noodles; soak until just tender (about 10 minutes) or as directed on the package. Drain and return to pot; toss with sesame oil and set aside.
2. Place a large skillet over medium heat and add the vegetable oil. When the oil is hot, reduce the heat to medium-lo and add the garlic and ginger; cook 1 minute, stirring constantly. Do not let the garlic brown.
3. Add the shrimp to the pan, increase heat to medium-high, and cook for 2 minutes, stirring often. When the shrimp are pink on the outside, add 1/2 cup of the water and continue cooking until they are opaque all the way through, about 2 minutes more. Remove the shrimp from the pan with a slotted spoon, add remaining water, lime juice, and soy sauce or fish sauce, and reduce until thickened, about 4 minutes. Remove from heat. Stir in cilantro. Divide noodles among 4 bowls, top with shrimp, drizzle with sauce, and garnish with peanuts, if desired.