1 tbsp sesame oil
½ small red pepper, deseeded and diced
1 onion, diced
150g shiitake mushrooms, chopped
300g minced pork or chicken
225g water chestnuts, drained and finely chopped
60g baby sweetcorn, cut into quarters
75g beansprouts
2 tbsp oyster sauce
2 tbsp soy sauce
2 tsp sweet chilli sauce
1 tsp rice wine vinegar
12 little gem lettuce leaves