Start by putting the sliced peppers on a board and roughly chop them into small dice.
Heat the oil and butter in a non-stick pan over a medium heat.
Add the diced onion and garlic and fry for 5 minutes, stirring occasionally.
Then add the diced peppers and chilli and continue frying for about another 7 minutes (until both softened but not coloured).
Add the sugar, ketchup, mustard, lime juice, clementine juice and seasoning.
Bring to the boil and then simmer under a lid for 15 minutes, stirring occasionally.
Serve warm (or cold if you wish) with burgers or any barbecued meats.
Keep any leftovers in a sealed container in the fridge for a few days or freeze the rest.