Mix together the papaya, ginger, garlic and green chilli pastes with chilli powder, garam masala powder, and salt and apply this on the cubes of mutton. Set aside in the refrigerator for three to four hours to marinate.
Pressure-cook the marinated mutton cubes with one cup of water till the pressure is released four times (4 whistles) or till half done.
Remove the lid when the pressure reduces and check if there is any liquid remaining. If yes, then cook till all the water evaporates. Remove from the pressure cooker and set aside.
Heat a grill and grill the mutton cubes till completely cooked. Baste with melted butter from time to time so that mutton does not dry out.
Once done, transfer to a plate and serve with the onion lachcha and the Mint Chutney.