Preheat the oven to 180°C fan.
Spray a casserole pan with low-calorie cooking spray and place on a low to medium heat.
Add the onion and gently fry for 8-10 minutes, until soft but not coloured.
Add the garlic and pesto and cook for another minute.
Add the rice and stir for 1-2 minutes until well coated.
Stir in the white wine vinegar, then add the stock.
Turn up the heat and stir until the stock is boiling. Cover with the lid and place in the oven for 25 minutes.
Remove from the oven. The stock should have been absorbed and the rice should be tender. Give a good stir and add the lemon juice, Parmesan and season with salt and black pepper.
Add the spinach to the top and replace the lid. Allow to stand for 5 minutes, then stir in the wilted spinach. Top with some extra Parmesan shavings if you want, and serve.