Cook the noodles 1-2 minutes less than the packet instructions, run under cold water, drain, set aside.
To make the sauce, in a small bowl, mix 1/2 cup water, corn starch, soy sauce, hoisin sauce, chili garlic sauce, ginger, garlic, and set aside.
Heat a a wok over high heat. Add 2 tablespoons of vegetable oil and heat until shimmering. Add the shrimp and stir-fry for 2-3 minutes, until just cooked. Remove the shrimp to a bowl.
Add the remaining 2 teaspoons of vegetable oil and stir-fry the scallions for 30 seconds, until fragrant. Add the red pepper and stir-fry for 3 minutes, then add the shrimp and the sauce. Stir together.
Toss noodles into wok, combine everything well until noodles are hot, no more than 3 minutes. Serve immediately.