Peel and finely chop the onion and garlic (press or chop the garlic as small as you can).
Wipe the mushrooms, if using, with kitchen paper to remove any dirt and slice finely.
Open the cans of tomatoes and beans. Drain the kidney beans through a colander and rinse with cold water.
Put the minced beef into the large bowl and add the onion and garlic. Mix together using a fork until the meat is thoroughly broken up.
Cover with a microwaveable lid or cling film, leaving a small area open to allow steam to escape.
Cook in the microwave on full power for five minutes. Remove from the microwave. Peel back the cling film and stir well with the fork, breaking up any clumps of meat.
Add the mushrooms, crumbled stock cube, chilli flakes or powder, tomatoes and beans to the meat and stir well.
Add a small amount of water to the empty tomato can, swirl around and add to the bowl. Season with black pepper to taste, if using.
Re-cover in the same way and cook on full power for five minutes. Remove the bowl and stir well.
Re-cover, return to the microwave and cook on full power for 10 minutes. Remove halfway through and stir well. Leave to stand while you cook the rice.
To cook the rice, boil the kettle. Add the rice to the sieve. Run cold water through the rice until the water runs clear and drain. Pour the rice into the other large microwave-safe bowl. Fill the same mug with boiling water twice and pour over the rice. Stir once and put into the microwave.
Microwave on full power for 10 minutes.
Remove the rice and stir. Return it to the microwave on full power for another minute.
Remove the rice and leave to stand for 1–2 minutes and then taste to check it is cooked. If it needs slightly more cooking add a small amount of water and cook for another two minutes.
Try adding one drained can of mixed pulses or 1 x 400g/14oz can of baked beans instead of red kidney beans, for a change.