Heat 1 tbsp olive oil in a large frying pan and cook the onions over a medium heat for 15 minutes until soft and browned; add half the garlic and cook for 1 minute. Meanwhile, cut the beef into thin strips, then make the salsa. For this, mix the chilli, remaining garlic, drained and rinsed kidney beans, tomatoes, coriander and the juice of ½ lime; season.
Transfer the onions to a bowl. Return the pan to a high heat, add ½ tbsp oil and brown the meat in batches. Put all the meat and the onions back in the pan, add the spices and cook for 1 minute.
Squeeze the remaining lime juice over the meat. Serve in taco shells with the lettuce and salsa.