In a small bowl or directly on a plate, whisk together chili oil and sweet soy sauce

Bring a pot of water to a rolling boil. Add the udon noodles and cook according to the package instructions (typically 1–4 minutes, depending on whether the noodles are fresh or frozen).

Drain the noodles and rinse with cold water to stop the cooking process. This ensures they remain perfectly chewy.

Place the cooked noodles in a large bowl. Pour the sauce over the noodles and toss until evenly coated.

Garnish with chopped green onion and a sprinkle of sesame seeds.