Heat a tablespoon of oil in a large saucepan over a medium heat. Add the onion and garlic and cook gently for about 10 minutes until softened. In another large frying pan heat the remaining oil, add the mince and fry until brown. Add the mince to the saucepan with the onion along with chilli, chilli powder, ground cumin, chopped tomatoes and stock or water. Mix well together. Season with salt and black pepper. Bring to a simmer then turn the heat down and cook for 30 minutes, stirring occasionally before adding the beans. Leave the saucepan on a low heat for another 10 minutes for the beans to heat through. Heat the oven to Gas Mark 4, 180°C (350°F) . To assemble the burritos: Divide the warm beef filling between the tortillas, roll to enclose the filling and secure with a cocktail stick. Place on an oiled oven tray, sprinkle with cheese and paprika. Bake for about 10 minutes until heated through. Remove from the oven and take out the cocktail sticks. Meanwhile make the guacamole: Mash the avocados in a medium bowl and stir in the remaining ingredients. Taste and season with salt and black pepper.
To Serve: Serve the burritos with the guacamole and soured cream.