Step 1

Heat a large skillet over medium heat. Add oil to pan. Add pork; cook 12 minutes, turning to brown on all sides. Place pork in a 6-quart slow cooker. Increase heat to medium-high. Add onions, cut side down, to skillet. Cook 5 minutes or until charred; transfer to slow cooker. Add stock, 4 cups water, and 2 tablespoons soy sauce to slow cooker. Remove stems from mushrooms; add stems to cooker. Reserve caps. Cover; cook on LOW for 7 hours.

Step 2

Remove pork from cooker. Let stand 5 minutes; shred. Strain liquid through a fine sieve into a bowl. Discard solids. Return liquid to slow cooker; increase heat to HIGH. Thinly slice mushroom caps. Add remaining 2 tablespoons soy sauce, mushroom caps, sesame oil, kombu, and ginger to slow cooker. Cook on HIGH for 20 minutes. Discard kombu and ginger. Add noodles to slow cooker; cook 5 minutes.

Step 3

Bring a pot of water to a boil. Carefully lower eggs into water; cook 6 minutes. Place eggs in a bowl of ice water for 2 minutes; peel and halve lengthwise. For each serving, place 3/4 cup noodles in a wide bowl; pour 1 cup broth over noodles. Top with pork, mushrooms, green onions, and chiles. Place 2 egg halves toward one side of bowl. Sprinkle with sesame seeds and nori.