Place a paella pan or large saute pan over medium heat and add the olive oil. Fry the chorizo to release some of the oil, about two minutes.
Add the onion and bell pepper and saute, stirring occasionally, until the onion is soft and translucent. Next, add the garlic, paprika, saffron, and cumin and saute for another minute until aromatic.
Stir through the tomato paste, and cook for a further 2 minutes. Add the rice and saute, stirring, for another 2-3 minutes until the grains are completely covered in the tomato and spices.
Pour in the stock, season with salt, and bring to a boil. Bring the heat down to low straight away and reduce to a simmer. Cook for 10-15 minutes. Don't stir the rice: it will release its starch and get gluggy. Resist the urge! Add a splash of water if the pan dries out.
When the rice is almost finished (about five minutes to go) arrange the shrimp/prawns on top of the rice, pressing into the rice with the back of a spoon. Cook until the seafood is just cooked all the way through and all of the liquid in the pan has evaporated.
Serve with lemon wedges, and bring the pan to the table for extra effect!
* If you can't find bomba rice, you can use another short-grain, starchy rice like Arborio.