Make the scissor noodles: Combine flour, 75g water, and salt. Mix until a firm dough forms. Add more water if needed. Cover and set aside.
Heat oil in a large pot over medium heat. Add onions and cook until translucent. Add carrots and cook for 4-5 minutes. Add leeks, thyme, ginger, and garlic. Cook for 1-2 minutes.
Pour in chicken stock and add chili flakes. Cook until vegetables are soft, about 5-10 minutes.
Press the noodle dough into a flat disk and rub with oil. Using scissors, cut thin strips of dough into the simmering soup. Continue until all dough is used.
Cook noodles for 3-5 minutes, or until cooked through. Stir in chicken and peas. Zest and juice lemon. Sprinkle with parsley.