Heat wok over high heat until hot. Add 1 tablespoon oil and the mushrooms and stir-fry 2-3 minutes until light golden and tender. Remove mushrooms to a plate, cover to keep warm. Reduce heat to medium-high. Add the remaining oil with the onion and coriander root and cook, stirring for 2 minutes until onion is soft.
Add curry paste and cook for 1 minute until fragrant. Stir in the coconut milk and stock. Bring to simmer; simmer for 5 minutes or until the sauce reduces slightly.
Add the mushrooms and fish and simmer for 5 minutes. Combine the fish sauce, lime juice and sugar and stir into the curry with the green onions, cook a further 3 minutes until fish is cooked through.
Top with chilli and coriander leaves, serve with lime wedges and rice.