Preheat the oven to 180C/350F/Gas 4.
Heat a heavy-based frying pan over a medium heat and fry the chorizo for 3-4 minutes, or until crisp. Remove the chorizo from the pan with a slotted spoon and set aside.
Fry the onion and garlic in the remaining oil for 3-4 minutes, or until soft.
Place the chorizo, onion, garlic, rice, tomatoes, butter and parsley into a well-buttered casserole dish. Season with salt and freshly ground black pepper.
Pour over the chicken stock, cover with a tight-fitting lid and bake in the oven for about 25-30 minutes, or until the rice is cooked.
Season the trout fillets with salt and freshly ground black pepper and squeeze over with the lemon juice.
Roast the trout pieces in the oven for 6-8 minutes, or until cooked through.
Serve the trout on top of the chorizo rice.