To make the tomato & onion salsa, toss onion, sugar and a pinch of salt in a bowl. Add vinegar and tomato, stirring to combine. Set aside.
Meanwhile, heat oil in a large frying pan over medium-high heat. Add mince, oregano and paprika and cook, breaking up mince with a wooden spoon, for 4 minutes or until browned. Add tomato paste and cook for 1 minute or until mixture has darkened slightly. Add beans and cook, stirring, for 4 minutes or until beans start to crisp up. Season.
Stir coriander through salsa. Squeeze lime over avocado, then top each half with mince mixture, a dollop of sour cream, lettuce, cheese and extra coriander. Serve with salsa and extra lime wedges.