Heat a large skillet over medium heat, then add the oil. Add the garlic and ginger and sauté until fragrant, stirring often.
Add leeks and green onions and sauté, stirring often, until the leeks have softened.
Add cooked noodles, gochujang, soy sauce and sesame oil, and toss to combine.
Divide equally into bowls. Top each serving with sesame seeds and green onions. Serve immediately.