Grind together the lemon grass, chillies, soy sauce, garlic, coriander (cilantro), parsley and galangal in a large pestle and mortar or a food processor. Set aside.
Heat the sunflower oil in a wok or large, heavy frying pan (skillet). Add the aubergine (eggplant) and stir over a high heat for 3 minutes, then add the mushrooms, stir and add the beans. Cook for 3 minutes, stirring constantly. Add the ground spice paste.
Add the coconut milk and lemon juice to the pan, bring to the boil and simmer for 2 minutes.
Serve immediately over rice, and garnish with the roasted peanuts.