Place chopped onion, tomato and capsicum in a medium bowl.
Trim the green cayenne chilli and deseed it. Finely chop the chilli and add it to the bowl.
Using a sharp paring knife, make vertical and horizontal cuts in the mango flesh to resemble a fine grid. Using a spoon, scoop out the finely cut flesh into the bowl.
Add lime juice, coriander leaves, salt and pepper. Mix gently.
Chill until ready to use or serve immediately with corn chips.