Spray a large pan with low-calorie cooking spray and set on a medium heat. Add the onion, garlic, and chicken, and fry for 8-10 minutes – until the onion has softened and the chicken is browned on all sides.
Turn the heat up, add the rice, and stir well. Add the mushrooms, stock cubes, white wine vinegar, and 100ml of the water.
Stir until the liquid has cooked into the rice, then turn the heat down to a simmer. Keep adding ladles of water and stirring – allowing each ladleful to be absorbed before adding the next.
Carry on adding water until the rice is soft – but with a slight bite. This will probably take around 30 minutes. Right before the rice is cooked through, add the peas to the pan.
Immediately pour into a serving dish – stirring in the parmesan and lemon juice. Then cover for 5 minutes or so, allowing the juices to fully soak in.