Cut off the ends of the beans and pull off any strings. Cut the tomatoes into pieces. Thinly slice the onion.
Put the onion in a saucepan with the lard and sauté over medium heat for about 5 minutes. When the onion is almost translucent, add the tomatoes and cook over medium heat for 15 minutes. Add the beans, season with salt and pepper, cover, and continue cooking over medium heat for