Pat the chuck roast dry with paper towels and season generously with salt and pepper.

Heat vegetable oil in a large skillet over medium-high heat. Sear the chuck roast on all sides until a deep brown crust forms, about 3-4 minutes per side. Transfer the seared beef to the basin of a 6-quart slow cooker.

In a medium bowl, whisk together the beef broth, soy sauce, mirin, and miso paste until the miso is dissolved. Pour the mixture over the beef in the slow cooker. Add the smashed garlic cloves and sliced ginger.

Cover and cook on low for 8 hours or on high for 4-5 hours, until the beef is fall-apart tender.

About 15 minutes before serving, cook the ramen noodles according to package directions in a separate pot. Drain well.

Carefully remove the beef from the slow cooker and shred or slice it. Strain the broth through a fine-mesh sieve to remove the garlic and ginger solids.

To assemble, divide the cooked noodles among six bowls. Top with the shredded beef. Ladle the hot, strained broth over the noodles and beef. Garnish with a soft-boiled egg half, sautéed mushrooms, sliced green onions, and a sprinkle of sesame seeds. Serve immediately.