1 Little Gem lettuce, leaves separated
100g/3½oz Portobello mushrooms, finely chopped
1/3 cucumber, sliced
½ small onion, finely chopped
2 tsp finely chopped fresh thyme (or ½ tsp dried thyme)
120g/4½oz cherry tomatoes, sliced
250g/9oz extra-lean beef mince (under 5% fat)