Beef and Snow Peas with Panfried Noodles

1 (9-ounces) package fresh Chinese-style noodles (or 8 ounces dried noodles)
2 tablespoons oyster sauce
1/2 tablespoon soy sauce
1/2 teaspoon sugar

2 teaspoons cornstarch

1/2 cup water
5 1/2 tablespoons vegetable oil, divided

1/2 pound snow peas, trimmed

3 scallions, finely chopped

2 tablespoons minced peeled ginger

1 pound flank steak, thinly sliced across the grain

Cook noodles according to package directions, then drain in a colander. Stir together oyster sauce, soy sauce, sugar, cornstarch, and water until smooth. Heat 1 tablespoon oil in a 10-inch nonstick skillet over medium-high heat until hot. Add noodles to skillet, pressing them with a rubber spatula to form a cake, and cook until underside is golden, 2 to 3 minutes. Flip cake over and drizzle 1 tablespoon oil around sides of cake, then cook until underside is golden, 2 to 3 minutes. Transfer noodle cake to a cutting board and cut into quarters. Heat 1/2 tablespoon oil in a wok or 12-inch heavy skillet over medium-high heat until it begins to smoke. Stir-fry snow peas with a pinch of salt until bright green, 1 to 2 minutes, then transfer to a plate. Add 2 tablespoons oil to wok and stir-fry scallions and ginger with 1/4 teaspoon salt 30 seconds. Add half of beef and cook, undisturbed, 45 seconds, then stir-fry until beef is just browned, 1 to 2 minutes more. Transfer to plate with snow peas. Add remaining tablespoon oil and cook remaining beef in same manner. Stir sauce mixture again, then add to wok and bring to a boil. Stir in beef and snow peas, then serve spooned on top of noodle cake.