Heat a large frying pan and add a little oil. Mix the minced beef and pork together. Season with salt and pepper and mix well to ensure the seasoning is evenly distributed. Fry the mince in the hot pan for 5–7 minutes until crisp and brown and broken down to a fine consistency. Drain the crisped mince in a sieve – this will help it stay crispy. Set aside.
Wipe out the pan and add a tablespoon of toasted sesame oil. Add the garlic, ginger and chilli. Fry with a pinch of salt and the sugar for 2 minutes. Add the drained mince and stir to mix.
Add the fish sauce and heat through. Stir in the lime zest and juice, then add the spring onions, stirring for 30 seconds. Turn off the heat.
Mix all the dressing ingredients together and adjust to taste.
To serve, spoon some of the mince mixture into the lettuce leaves, drizzle with a little dressing and serve.