Bring a large pot of salted water to a boil. Add the fresh ramen or udon noodles, cooking according to package instructions until tender but still chewy, about 3-5 minutes. Drain and rinse under cold water. Set aside to air dry.

In a medium bowl, combine 2 tablespoons of gochujang, 2 tablespoons of soy sauce, 1 tablespoon of brown sugar, 1 teaspoon of sesame oil, and 2 minced garlic cloves. Whisk together until smooth, adjusting with a splash of water if necessary.

Heat 1 tablespoon of vegetable oil in a large skillet over medium-high heat. Add the boneless chicken thighs, cooking for about 6-8 minutes until golden brown and reached an internal temperature of 165°F (75°C). Remove from skillet and set aside.

Pour the prepared gochujang sauce into the same skillet and return the chicken. Stir to coat the chicken evenly in the sauce and cook for an additional 2-3 minutes.

Add the cooked noodles to the skillet and toss everything together gently to ensure the noodles are coated in the sauce. Cook for an additional 1-2 minutes.

Spoon the Korean Spicy Chicken Noodles into bowls and garnish with sliced scallions and toasted sesame seeds. Serve immediately.