Put the onion, ginger, garlic, curry powder and half the coriander in a small blender with 1-2 tbsp water until it comes together in a paste. Cook the rice to pack instructions.
Heat the oil in a large, lidded frying pan over a medium-high heat and fry the paste for 3-4 mins until fragrant. Add the coconut milk, season and bring to a simmer. Nestle the fish fillets into the sauce and add the green beans around them (don’t worry if not everything is submerged).
Cover and simmer for 10 mins, still on a medium-high heat, then remove the lid, stir gently and cook for another 5 mins or until the fish is cooked through, the green beans are tender and the sauce has thickened slightly (it will still be quite thin). Don’t stir too much or the fish will break up. Squeeze over the lime juice and check for seasoning.
Fluff up the rice, divide between bowls and spoon over the curry. Scatter with the reserved coriander to serve.