Pork and chorizo burgers

Name: Pork and chorizo burgers
Ingredients: 1 onion, finely chopped; 1 tbsp olive oil; 100g/3½oz cooking chorizo; 300g/10½oz pork mince; 2 tbsp tomato ketchup; 1 tbsp Worcestershire sauce; ½ tsp sweet smoked paprika; 2 tbsp coriander leaves, chopped; 2 free-range eggs; 6 water biscuits, finely crushed; ½ tsp table salt; salt and freshly ground black pepper; 6 tbsp mayonnaise; 1 red chilli, finely chopped; 2 tsp sriracha sauce (hot chilli sauce); 8 pickled gherkins, finely chopped; 4 slices cheddar; 50g/1¾oz rocket or lettuce leaves; 4 burger buns