Finely chop the onion. Thinly slice the cucumber. Trim the lettuce, then thinly slice the leaves. Coarsely grate the cheese. Combine 1 tbs white vinegar and 1 tsp sugar in a bowl. Add the cucumber and toss to coat. Set aside to pickle, tossing occasionally, until needed.
Step 2 — Brown beef mince
Heat 2 tsp olive oil in a medium frypan over medium heat. Cook the onion, stirring, for 3-4 mins until softened. Increase the heat to high, add the beef mince and cook, breaking up the lumps with a spoon, for 3-4 mins until browned.
Step 3 — Add flavourings
Add the barbecue seasoning, barbecue sauce and 2 tbs water to the mince mixture. Cook, stirring, for 30 secs-1 min until slightly thickened. Remove the pan from the heat. Taste, then season with salt and pepper.
Step 4 — Grill nachos
Preheat the grill to high. Line an oven tray with foil. Spread the corn chips over the lined tray. Spoon over the mince mixture and scatter with the cheese. Grill for 5 mins or until the corn chips are toasted and the cheese is melted.
Step 5 — Serve up
Scatter the drained pickled cucumber and lettuce over the nachos and dollop with the burger sauce. Pop the nachos on the table for everyone to help themselves. Enjoy!
Step 6 — Make it spicy
If you like a kick of heat, scatter over thinly sliced fresh chilli or a pinch of chilli flakes just before serving.