Topping
1 ripe avocado, peeled and mashed
2 tomatoes, seeded and chopped 1 small clove garlic, crushed
1 tbsp lime or lemon juice
Filling
1 tbsp oil
1 shallot, finely chopped
1/2 green pepper, chopped
1 tsp ground cumin
1/2 red or green chilli pepper, seeded and finely chopped
4 tbsps tomato puree
6 tbsps water
Salt and pepper
120 g (4 oz) cooked, peeled prawns, roughly chopped
4 taco shells