Preheat oven to 200°C (or 180°C fan bake).
Place tortillas into 2 oven-proof bowls and push in to create a bowl shape. Bake in the oven for 10-12 minutes, until golden and crispy. Remove from oven and set aside.
Heat oil in a frypan on a medium-high heat. Cook beef and measure of spices, breaking up beef as it cooks, for about 5 minutes, until browned. Add beef stock and continue to cook for 2 minutes, until slightly reduced. Season with salt and pepper.
Grate cheese, shred lettuce and dice tomato.
Fill nacho bowls with beef, cheese, lettuce and tomato. Drizzle over pebre salsa, sprinkle with chilli flakes (if using) and garnish with coriander leaves.