Put the peppercorns, garlic and Thai chilli (if using) in a pestle and mortar and pound to a rough paste.
Cut up the vegetables and set aside
Heat the oil on medium-high heat , add the paste and stir fry for a minute or so
Add the pork, keeping it moving and fry for a minute. Go in with the squash and onions, turn up the heat to high and cook for another couple of minutes. Make sure it constantly moving. At this point, you should have a little colour on the pork.
Add the sugar, oyster, soy and enough water to loosen it all up and make a sauce. turn the heat down a bit and let the pork cook through in the sauce. This won't take long!
Throw in the Thai basil and turn off the heat. Let the basil wilt in the residual heat from the wok.
Check for seasoning, adding a little soy or sugar if you think it needs it.
Serve on steamed Jasmine rice with a squeeze of the lime.