Heat the sunflower oil in a saucepan over a medium heat and cook the red onion, finely chopped, for 5 mins until slightly softened. Add the chopped tomatoes, garlic clove, finely grated, sweet smoked paprika, tomato purée, red wine vinegar and red chilli, if using. Season and simmer for 15-20 mins until the mixture has cooked down and thickened slightly.