In a large pot, bring water to a boil and cook udon noodles according to package instructions. Drain and set aside.

In a separate pot, heat vegetable oil over medium heat. Add sliced pork belly and cook until browned and crispy. Remove from pot and set aside.

In the same pot, add sliced onion and minced garlic. Cook until onions are translucent.

Add chicken broth, soy sauce, mirin, and sake to the pot. Bring to a simmer.

Add cooked udon noodles and sliced pork belly back to the pot. Stir to combine and let simmer for a few more minutes.

Serve hot, garnished with sliced green onions and nori seaweed.