Bring a medium pot of lightly salted water to a boil. Place a wire-mesh strainer in the sink. Thoroughly rinse produce and pat dry. Cut mushrooms into small ½" dice. Coarsely chop peanuts. Trim and slice green onions thinly on a bias (angle). Mince garlic. Remove tough outer layer of lemongrass by peeling away with your fingers, exposing the tender stalk underneath. Very finely mince bottom 3" of stalk and discard the rest. Lemongrass is an extremely fragrant and flavorful herb with a citrus flavor used in many Asian cuisines.

Place noodles into boiling salted water and cook until al dente (6-10 minutes). Strain and return to pot. Toss with half the sesame oil. Tossing with sesame oil helps flavor the noodles, but also keeps them from sticking. If noodles get sticky, add warm water 1 Tbsp. at a time until they loosen up.

Place a medium pan over medium-high heat. Add 1 Tbsp. olive oil and chopped mushrooms. Cook, stirring occasionally, until moisture begins to cook out and mushrooms start to brown and sizzle in pan, about 5-7 minutes.

Add half the green onion, garlic, minced lemongrass, and ginger to pan and cook until fragrant (about 1 minute). Add half the peanuts, rice vinegar, ¼ cup water, and soy sauce and cook for 2-3 more minutes. Season to taste with a pinch of salt and pepper.

Transfer half the mushroom mixture to a plate. Add cooked noodles and red cabbage to remaining mushroom mixture in pan and toss to coat. Season with remaining sesame oil (to taste). Sesame oil, made from sesame seeds, is widely used in Asian cuisines. It has a delicious but powerful flavor, so use it sparingly.

Divide noodles between two bowls. Top noodles with reserved cooked mushrooms, remaining green onions, and remaining peanuts. Serve immediately.