Bring a medium pot of water to a boil. Remove the pot from the heat, add the noodles, and soak them until tender, about 5 minutes. Drain, transfer to a baking sheet lined with paper towels, and pat dry. Toss the noodles with 1 Tbs. of the sesame oil.
Toss the chicken with the remaining 1 tsp. sesame oil, the sherry, and 1/4 tsp. salt.
In a small bowl, mix the hoisin sauce, soy sauce, and vinegar.
Heat 1-1/2 Tbs. of the canola oil in a 12-inch nonstick skillet over medium-high heat until shimmering hot. Add the mushrooms and cook, stirring, until softened and lightly browned, about 2 minutes. Add the chicken and cook, stirring, until it just loses its raw color, about 2 minutes. Add the spinach and cook, stirring, until it wilts, about 1 minute. Add the hoisin mixture and cook, stirring, until the chicken is cooked through, about 1 minute. Transfer to a bowl.
Wipe out the skillet with a paper towel. Heat the remaining 1-1/2 Tbs. oil over medium heat. Divide the noodles in half and spread them in the pan, forming two oblong cakes (if they become entangled, just cut them apart with scissors). Sprinkle lightly with salt and cook until the bottoms are lightly browned and crisp, 4 to 5 minutes. Flip, sprinkle lightly with salt, and cook until the second sides are browned and crisp, about 4 minutes more. Transfer to serving plates, top with the chicken, and serve with chile sauce, if using.