Heat the oil in a deep saucepan and fry the chopped onion over a medium heat until tender. Add the garlic and tomato purée, stirring for 1-2 mins until combined. Sprinkle in the spices and cook for another 1 min.
Tip in the chopped tomatoes, half fill the can with water, and add to the pan. Pour in the stock and simmer on a medium heat for 10-15 mins, uncovered. Season, then whizz using a hand blender until smooth. Add the beans and red pepper, and cook for another 15 mins until the pepper is tender.
Serve in bowls topped with a small pile of tortilla chips and a lime wedge.