De-seed the chillies and chop finely. Peel the onion and garlic, chop roughly.
Put the onion, chilli, garlic & herbs into a small food processor and pulse for a few seconds until you get a rough paste.
Mix this paste with the minced beef, season with salt & pepper and combine well.
Divide into four portions, form balls then patties between your palms.
If you have time rest the patties for 2-4 hours in the refrigerator. If not, chill them while you prepare the chimichurri sauce.
Chimichurri sauce: Roughly chop the onion, garlic and chillies, then in a small blender pulse for a few second. Squeeze over the lemon juice, then add the grated zest of half the lemon. Add the rest of the ingredients and blend until you get a coarse paste. Spoon the sauce in a small bowl, set aside.
Heat the barbecue, grill or griddle pan. Brush the patties with little oil.
Cook the patties on both sides for one minute to seal, then for about 5 minutes turning occasionally, depending on how well-done you like your burger. For the last 2-3 minutes cover them with a slice of cheese if you want a cheeseburger.
Transfer the burgers to a plate and rest them for 5 minutes (under cover).
In the meantime cut the rolls or buns in half then grill them for 1-2 minutes. Put half teaspoon of chimichurri sauce on the lower half, place the burger on it, then spoon more sauce on the top.
Enjoy!