Preheat the oven to 180C/160C fan/Gas 4.
Heat the oil in an ovenproof dish or pan on the hob. Add the onion and cook for 3-4 minutes until soft.
Add the garlic and drained mushrooms. Cook for 2 minutes.
Stir in the uncooked rice, chopped tomatoes, vegetable stock, mixed herbs, salt and pepper. Bring to a simmer.
Cover with a lid or foil and transfer to the oven. Bake for 30 minutes.
Remove from the oven and stir. The rice should be tender and most of the liquid absorbed.
Sprinkle the grated cheese over the top. Return to the oven uncovered for 5 minutes until the cheese is melted and golden.
Serve straight from the dish.