Mash the chicken tikkas in a masher.
Add onion, green capsicum, coriander leaves, green chutney and chaat masala and mix. Add mayonnaise and mix well. Butter the bread slices on one side only.
Spread the filling evenly over four slices and cover with another slice each. Apply a little butter on the outer sides of the sandwich and place them one by one in the preheated grill. Grill till golden. Cut into triangles and serve immediately. You can serve the sandwiches without grilling too.
In that case trim the edges and cut into triangles and serve.