Heat oil in a deep pan, and sauté garlic and curry paste till fragrant. Add in onions and chicken/tofu, and saute till lightly browned.
Add in coconut milk, stock and lemongrass, and let it come to a boil on low heat.
Add in mushrooms and noodles, and cook covered till noodles are tender and done. Stir in bok choy, cover and cook for 5 minutes.
Season with salt and pepper, add garnish with coriander leaves, chillies and a dash of lemon juice. Ladle in large bowls and serve piping hot.