Heat oil in a large, deep frypan with a lid. Add onion and garlic and saute over gentle heat for 3-4 minutes. Add chorizo and cook for 2 minutes. Add rice and cook for a further minute. Increase heat, add wine and allow it to bubble up. When the wine has been absorbed, add the tomatoes and cook, stirring, for 2 minutes.
Add stock to pan and bring to the boil, reduce heat to the lowest setting, place a lid on the frypan and cook for 12-15 minutes until all of the liquid has been absorbed and the rice is cooked.
Stir through prawns and cook for a further 2-3 minutes until they are tender. Add a little more water if it is looking too dry. Just before serving, stir through baby spinach and garnish with spring onions.