Preheat oven to 230°C. Line a large pizza tray with baking paper. Arrange potato minis in a single layer and bake for 20 minutes, turning over halfway through cooking time, or until golden and crisp.
Remove from oven and reduce oven temperature to 200°C. Top with three-quarters each of chipotle cheddar and tasty cheese and taco sauce. Top with chicken and remaining sauce and cheese. Bake for 10 minutes.
Meanwhile, combine tomato, cucumber and onion in a small bowl. Top nachos with sour cream, salsa and coriander sprigs. Serve nachos immediately.