Place chicken in a large bowl of salted water. Poach chicken for about 6-7 minutes or until cooked through. Drain. Shred chicken. Set aside.
Meanwhile, heat oil in a large skillet or frying pan over medium-high heat.
Add onions, ginger, garlic, coriander stem, and green chillies. Sauté, stirring occasionally, for about 2-3 minutes or until the onions are soft.
Add spices. Cook, stirring, for about 1 minute or until aromatic.
Add chicken broth (stock) and lemon juice. Stir to combine.
Season with salt. Simmer for about 2-3 minutes.
Add vegetables, soy sauce and cooked chicken. Cook, stirring occasionally, for about 2-3 minutes.
Garnish with coriander (cilantro) leaves and spring onions (scallions).
To serve, divide noodles among 4 bowls. Top with soup and chili paste.