1.Preheat oven to 200°C.
2.Spray tortillas on both sides with oil; press into holes of a 6-hole Texas muffin pan. Bake for 8 minutes or until browned lightly.
3.Heat olive oil in a large frying pan over high heat; cook three-quarters of the onion, stirring, until softened. Add beef; cook, stirring, until browned. Add beans and taco sauce to pan. Simmer, uncovered, for 3 minutes or until thick. Season to taste.
4.Make guacamole; peel and coarsely mash avocado in a small bowl with a fork; stir in remaining onion, coriander and juice. Season to taste.
5.Spoon beef mixture into tortillas; top with guacamole. Serve with sour cream and lime cheeks, if you like.