Slice chicken thighs into thin strips.Heat oil in a pan and cook chicken until browned.Add soy sauce and garlic, stirring to coat.Stir in gochujang, brown sugar, and water. Simmer until thickened.Cook ramen noodles, drain, and add to the pan.Toss noodles with the sauce and simmer for 1 to 2 minutes.Add butter and mix until glossy.Garnish with green onions and chili flakes.