Mix the beef mince, garlic, salt and pepper together in a bowl. Then roll the mince into about 6 balls using your hands. Rub the beef with olive oil. Cook in a hot frying pan for 8-10 minutes, turning regularly, until golden-brown and cooked through.
For the guacamole, put all of the guacamole ingredients in a bowl and mash to a rough mixture with a fork.
Spread the tortillas with the guacamole, fill with the hot beef and add some yoghurt. Squeeze over a little more lime juice to taste, add a few lettuce leaves, then roll the tortilla up.