Heat the oil in a large saucepan over a medium heat. Add the onion, celery and carrots, then cook for 5–6 minutes, stirring occasionally, until the onion begins to soften. (I also added some leek as I had some about that needed using)
Add the garlic. Cook for another 2 minutes.
Stir in the smoked paprika and chilli flakes. Cook for 30 seconds, just until the spices smell fragrant. Take care not to let them burn.
Pour in the chopped tomatoes and vegetable stock. Stir well and bring to a gentle boil.
Reduce the heat, partially cover the pan and simmer for 12–15 minutes, or until the carrots are tender.
Add the drained mixed beans and simmer for a further 5 minutes, until piping hot.
For a thicker soup, blend two or three ladlefuls until smooth and stir them back into the pan. Alternatively, briefly use a stick blender while leaving plenty of beans and vegetables whole.
Season with salt and black pepper. Ladle into warm bowls and finish with your favourite toppings.