How to Make It
In a large pot of boiling salted water, cook the chow mein noodles until al dente, about 8 to 9 minutes. Drain the noodles, reserving 1/2 cup of the cooking water. Return the chow mein noodles to the pot and toss with the sesame oil.
Meanwhile, in a medium skillet, heat the peanut oil until shimmering. Add the garlic and cook over moderate heat, stirring just until fragrant, 30 seconds. Add the peanut butter, vinegar, soy sauce, ginger, sugar and crushed red pepper and stir to form a paste. Add the stock and stir until smooth; season with salt.
Pour the peanut sauce over the noodles. Add the prosciutto and scallion and toss until the noodles are coated. Add about 1/4 cup of the reserved cooking water and toss until the sauce is creamy, adding more water as needed. Transfer the noodles to bowls, garnish with the cucumber and serve.