In a small bowl, whisk together the gochujang, peanut oil, sesame oil, soy sauce, mirin, and water. Set aside.
Brown the beef in a large skillet over medium-high heat, breaking up the meat as it cooks. Add the garlic and cook for 1 minute.
Add the gochujang mixture and bring to a simmer. Reduce the heat to low and simmer for 5 minutes.
Meanwhile, cook the ramen noodles according to the package directions. Drain, reserving 1/4 cup of the cooking water, and transfer the noodles to the skillet with the beef. If you want a thinner sauce, add some of the cooking water.
Add the green onions and toss to combine.
If desired, top with sesame seeds and gochugaru and serve.