Heat a wok over high heat until hot. Add half the oil and swirl to coat. Add half the mushrooms and stir-fry 2-3 minutes until golden. Transfer to a plate, repeat with remaining oil and mushrooms.
Reheat heat to medium, add the laksa paste and stir for 1 minute or until aromatic and the oil from the paste separates. Add the stock and coconut milk and bring to the boil. Boil gently 5 minutes to reduce and concentrate the flavours.
Meanwhile, place noodles into a heatproof bowl. Cover with boiling water and set aside for 3 minutes until almost tender. Drain and keep warm.
Add the mushrooms, reduce heat to medium and simmer uncovered 10 minutes until soup has reduced slightly. Combine the palm sugar and lemon juice and stir into the soup.
Divide the noodles between serving bowls. Pour over the soup then top with sprouts, cucumber, mint, coriander leaves and shallots and chili if using.