Heat oil in a pan and fry the garlic and onion until the onions are translucent and soft. Add the cumin and chilli flakes and fry for 2 minutes. Leave to cool slightly, then place in a bowl with the beef, sun-dried tomato paste, coriander, salt and black pepper to taste. Mix thoroughly, then divide into 4 equal portions and shape into burgers.
Brush the grill or pan with a little oil and cook the burgers for about 8 mins, turning once. This will result in a medium-rare burger (increase cooking time to taste).
Put butter on buns and lightly toast in a frying pan. Place the burger in the toasted bun. Add lettuce and sauces as required.