Cook udon noodles according to package instructions. Drain and set aside.
In a large heat-proof bowl, combine diced shallot, minced garlic, soy sauce, dark soy sauce, gochugaru, chili crisp, rice vinegar, sesame oil, sugar, and kecap manis if using. Mix well.
Heat oil in a small pan until it reaches approximately 400°F (oil should shimmer and bubble when a drop of water is added).
Carefully pour the hot oil over the sauce mixture. The mixture will sizzle and bubble, blooming the aromatics and spices.
Add the cooked udon noodles to the bowl and toss thoroughly until evenly coated with the sauce.
Transfer to serving bowls and garnish with chopped green onions and crispy garlic before serving immediately.