Peel and finely chop your onion. Peel and crush the garlic. Deseed the peppers, and chop them into bitesize pieces. Run a sharp knife very carefully along the length of the chorizo sausage, then peel off the skin. Slice the chorizo into rounds, then chop these into half moons. Grate the cheese.
Put a non-stick pan on the hob on a medium heat, and once it's hot, throw in the chorizo and cook for 3-5 minutes (there's no need to add extra oil, as the chorizo will release flavoured oil as it cooks). Add the onions and peppers to the chorizo, and fry for 5-7 minutes until the peppers are soft and the onions are translucent. Add the garlic, and cook for another 2-3 minutes.
Throw your rice in the pan, and use a wooden spoon to stir it until everything is coated in the oil. Pour in the lager, and let it cook down for 3-5 minutes. Stir in the the tomato puree and smoked paprika.
Pour a ladleful of stock into the pan, and use the wooden spoon to stir it in. Keep stirring until you can't see any liquid, then add another ladle of stock and stir again. Keep adding ladles of liquid (one at a time) and stirring, until the rice is cooked through and the sauce is creamy: approx. 25-30 minutes. Don't worry if you don't use all the stock.
Take the pan off the heat, and stir through the Parmesan until melted. Check the seasoning, and add salt and pepper as needed. Slice the lemon in half and squeeze the juice over the risotto, give everything a final stir, and serve immediately.
If you're vegetarian, you could omit the chorizo and substitute with some butternut squash chunks, or even just double the amount of peppers. Make sure you also double the quantity of smoked paprika so you keep the flavour.
If you're vegan, you'll also need to substitute the Parmesan for a vegan hard cheese. A lot of lagers are vegan-friendly, so just make sure you check the bottle before using (here's a list for any UK readers).
For both: add a bit of vegetable oil to the pan before cooking the onions.