Bring the rice to the boil in 400 ml salted water, cover and leave to soak for 15-20 minutes.
Wash the fillet, pat dry and cut into strips. Cut the onions into rings, drain the corn and beans.
Mix rice with fillet, onions, corn and beans, season with salt, pepper and thyme, place in a greased baking dish. Whisk the cream with the grated cheese and pour over the rice mixture. Bake until golden brown for about 40 minutes.