Heat the olive oil in a large pot over medium-high heat. Season the pork with salt and pepper to taste, then place into the hot oil. Cook until golden brown on all sides, about 7 minutes. Once browned, remove the pork and set aside. Reduce heat to medium and stir in the onion and garlic. Cook and stir until the onion has softened and turned translucent, about 5 minutes.
Return the pork to the pot and stir in the green chillies, chopped tomatoes with juice, tomatillo salsa and chicken stock. Season with oregano and cloves. Bring to a simmer over medium-high heat, then reduce heat to medium-low, cover and simmer 20 minutes.
After 20 minutes, remove 500ml of the soup (ensure there are no pork cubes in it) and pour into a liquidiser. Hold down the lid of the liquidiser with a folded tea towel and carefully start the liquidiser, using a few quick pulses to get the soup moving before leaving it on to puree. Puree until smooth, then pour back into the cooking pot. This will create a thicker texture for your chilli and will eliminate some of the chunky bits of chillies. Continue to simmer, stirring occasionally until the pork is very tender, at least 35 minutes more.
Tinned roasted green chillies and tomatillo salsa can be purchased online.