Heat oil in a large frying pan over medium heat. Add onion. Cook, stirring, for 2 to 3 minutes or until softened. Increase heat to high. Add mince. Cook, breaking up with a wooden spoon, for 5 minutes or until browned.
Add seasoning. Cook, stirring, for 1 minute or until fragrant. Stir in stock and tomato paste. Bring to the boil. Reduce heat to low. Simmer for 2 minutes or until slightly thickened.
Heat tortillas following packet directions. Place tortillas on work bench. Top each with mince mixture, avocado, tomato and lettuce. Fold up to enclose filling. Serve.