Boil noodles until al dente. Reserve ⅓ cup pasta water, then drain noodles. Rinse briefly under cold water for 5–10 seconds.
In a heatproof bowl, add chili flakes, garlic, green onions, sesame seeds, sugar, peanut butter, and gochujang.
Heat avocado oil in a small pot until very hot (about 350°F). Carefully pour the hot oil over the bowl ingredients to sizzle everything together.
Add soy sauce and mix well.
Slowly stir in reserved pasta water until the sauce becomes creamy and slightly loose. Season with a pinch of salt.
Add noodles and toss until fully coated.
Garnish with extra green onions and sesame seeds if desired. Eat immediately.