Boil the noodles according to package directions until just al dente. Drain, reserving about ½ cup of pasta water, and set aside.
In a large pan over medium heat, melt the butter over medium heat then add minced garlic and cook for 1-2 minutes until fragrant.
Add the miso paste, soy sauce, rice vinegar, sesame oil, and sugar to the pan, stirring well to combine. Pour in the reserved pasta water a little at a time until you reach a creamy, glossy consistency. Turn the heat to low.
Add the noodles to the pan, tossing them in the miso garlic sauce until well coated for about 1 min, allowing the sauce to thicken and cling to the noodles.
Transfer noodles to a plate and garnish with green onions, sesame seeds, and chili oil. Add a lime wedge on the side for a pop of brightness.
Optionally top with a fried egg, crispy tofu, or sautéed veggies.
