Cook noodles: Boil noodles according to package directions. Drain and set aside.
Sauté garlic: In a large pan, heat shiitake mushroom oil over medium heat. Add minced garlic and cook until fragrant and lightly golden, about 30 seconds to 1 minute.
Make sauce: Add soy sauce, brown sugar, and chili flakes. Stir until sugar dissolves.
Toss noodles: Add cooked noodles, noodle water & spices to the pan and toss until evenly coated in the sauce.
Finish: Remove from heat and top with green onions & sesame seeds! Add chili oil if you'd like it spicier!