Place chicken cubes in a bowl, add salt, ½ tsp Kashmiri red chilli powder and juice of ½ lemon and mix well.
Set aside in a refrigerator to marinate for 15 minutes.
Mix together hung yogurt, garlic paste, ginger paste, salt, ½ teaspoon Kashmiri red chilli powder, garam masala powder and mustard oil in a bowl.
Add chicken and mix well. Set aside in the refrigerator to marinate for 3-4 hours.
Halve the burger buns horizontally. Cut onion into thick roundels.
Put some butter on a heated griller and place the onion roundels on it and grill till lightly browned.
Mix together mayonnaise and green chutney in a small bowl. Remove onion from the griller and place in a bowl.
Arrange chicken pieces on the griller, drizzle a little oil and cook till the chicken is cooked and golden.
Apply mayonnaise-green chutney over all the burger halves.
Tear a few lettuce leaves and place over the bottom halves.
Arrange the chicken tikkas over the lettuce and place the onion roundels over them.
Cover with the top halves of the burgers and press lightly. Serve immediately.