Slice the top of each tomato and using a teaspoon scoop out the flesh and seeds onto a board, taking care not to cut through the skin of the tomato. Discard the central core and roughly the chop the flesh and seeds. Scrape into a small bowl, keeping as much juice as possible. Set aside the shells and tops.
Heat the oil in a large nonstick saucepan and fry the onion over a low heat for 6-8 minutes until soft but not coloured, stirring regularly. Add the garlic and cook for a minute longer. Increase the heat and add the courgettes and mushrooms to the pan. Cook for 5 minutes stirring continuously until the vegetables have started to take on a little colour.
Preheat the oven to 200°C/fan 180°C/Gas 6. Add the chopped tomato flesh and seeds, stock and thyme to the vegetables and stir in the rice. Bring to a simmer, cover and leave to cook for 8 -10 minutes or until the rice is not quite cooked but all the liquid has been absorbed, stirring occasionally.
Discard the sprigs of thyme, stir in the parsley and season the rice with lemon juice, salt and black pepper. Stuff each tomato with the rice filling and place in a small shallow oven-proof dish; they should fit fairly snugly. Put the tops back on the tomatoes and bake in the oven for 30 minutes or until the tomatoes are tender. Serve with a lightly dressed rocket salad.
*Some vegan products may only be available in limited stores.
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